Image pickup system

ABSTRACT

The invention provides a zoom lens system much more reduced in size and cost than ever before and best-suited for use on portable information terminals of small size. The zoom lens system comprises, in order from an object side thereof, a first lens group G 1  having positive refracting power and designed to be fixed during zooming, a second lens group G 2  having negative refracting power and designed to move from the object side to an image plane side of the system for zooming from a wide-angle end to a telephoto end of the system, a third lens group having refracting power and designed to move from the image plane side to the object side for zooming from the wide-angle end to the telephoto end, and a fourth lens group G 4  having positive refracting power and designed to be movable during zooming. Condition (1) with respect to the power of the third lens group G 3 , condition (2) with respect to the amount of zooming movement of the third lens group G 3  or condition (3) with respect to the composite power of the third and fourth lens groups G 3  and G 4  and condition (10) with respect to the actual value of the back focus are satisfied.

This application claims benefit of Japanese Application(s) No. Hei11-316827 filed in Japan on Nov. 8, 1999, the contents of which areincorporated by this reference.

BACKGROUND OF THE INVENTION

The present invention relates generally to a zoom lens system and animage pickup system using the same, and more particularly to a compactyet low-cost zoom lens system for cameras using an electronic imagepickup means, for instance, camcorders, digital cameras, surveillancemonitor cameras and cameras incorporated in portable telephones or PCs.

SUMMARY OF THE INVENTION

For zoom lens systems which belong to this field and are reduced in sizeand cost for consumer-oriented purposes, there has been proposed afour-group zoom lens system of +−++ construction in order from itsobject side, as shown in JP-A's 4-43311 and 4-78806. In this zoom lenssystem, the first and third lens groups are fixed during zooming, andthe second lens group having negative power moves on an optical axis forzooming while the fourth lens group moves on the optical axis forcorrection of fluctuations of an image plane position with zooming. Inzoom lens systems as set forth in JP-A's 6-94997 and 6-194572, on theother hand, the third lens group is moved from the image plane side tothe object side for zooming from the wide-angle end to the telephoto endfor the purpose of aiding in zoom action, thereby achieving further sizereductions. These publications show zoom lenses having a relatively highzoom ratio of the order of 8 to 12. For a zoom lens system reducedexclusively in size and cost at the expense of zoom ratios, however,such prior art systems are still less than satisfactory because nosufficient size reductions are achievable thanks to an increased numberof lenses.

In the zoom lenses shown in the aforesaid JP-A's 6-94997 and 6-194572, asubstantial portion of their zooming action is assigned to the secondlens group. To keep a substantially constant image point in this case,the transverse magnification of the second lens group must be in theneighborhood of −1 in the range from the wide-angle end to the telephotoend of the system. When further size reductions are intended by makingthe zoom ratio smaller than this, however, the amount of movement of thesecond lens group can be so reduced that the space margin between thefirst and second lens groups can be cut to the bone, thereby achievingefficient size reductions.

To perform zooming while the second lens group has a transversemagnification in the neighborhood of −1 with a narrower spacing betweenthe first and second lens groups, however, it is required to increasethe power of the first lens group with respect to the second lens group.This in turn causes an entrance pupil to be located at a fartherposition and so the height of off-axis rays passing through the firstlens group to increase, resulting unavoidably in an increase in the sizeand, hence, the thickness of the first lens group. It is also requiredto increase the curvature of each lens in the first lens group. Toensure each lens of sufficient edge thickness, it is then necessary toincrease the thickness of each lens in the first lens group.

SUMMARY OF THE INVENTION

In view of such states of the prior art as explained above, an object ofthe present invention is to provide a zoom lens system much more reducedin size and cost than ever before, and an image pickup system using thesame.

One specific object of the present invention is to provide a four-groupzoom lens system which can have the desired zoom ratio while its size isreduced without increasing the power ratio of the first lens group withrespect to the second lens group.

Another specific object of the present invention is to achieve a compactzoom lens system suitable for use on digital cameras, and cameras addedto portable telephones and PCs, which is designed in such a way as toprovide a nearly telecentric exit beam with image pickup devices such asCCDs and CMOSs in mind. This zoom lens system ensures the desired backfocus enough to receive a low-pass filter, a beam splitter, etc. ifrequired, and achieves improved image-formation capability with areduced number of lenses.

According to one aspect of the present invention, these objects areachievable by the provision of a zoom lens system characterized bycomprising, in order from an object side of the zoom lens system, afirst lens group having positive refracting power and designed to befixed during zooming, a second lens group having negative refractingpower and designed to move from the object side to an image plane sideof the zoom lens system for zooming from a wide-angle end to a telephotoend of the zoom lens system, a third lens group having positiverefracting power and designed to move from the image plane side to theobject side for zooming from the wide-angle end to the telephoto end,and a fourth lens group having positive refracting power and designed tobe movable for zooming, wherein the following conditions are satisfied:

0.5<|F ₂ /F ₃|<1.2  (1)

2.5 mm<f _(B)(min)<4.8 mm  (10)

where F_(i) is the focal length of an i-th lens group and f_(B(min)) isthe length, as calculated on an air basis, of the final surface of alens having power in said zoom lens system to an image plane of saidzoom lens system, representing a figure at which said zoom lens systembecomes shortest in a whole zooming space.

According to another aspect of the present invention, there is provideda zoom lens system characterized by comprising, in order from an objectside of the zoom lens system, a first lens group having positiverefracting power and designed to be fixed during zooming, a second lensgroup having negative refracting power and designed to move from theobject side to an image plane side of the zoom lens system for zoomingfrom a wide-angle end to a telephoto end of the zoom lens system, athird lens group having positive refracting power and designed to movefrom the image plane side to the object side for zooming from thewide-angle end to the telephoto end, and a fourth lens group havingpositive refracting power and designed to be movable for zooming,wherein the following conditions are satisfied:

0.49<|L ₃ /L ₂|<1  (2)

2.5 mm<f _(B)(min)<4.8 mm  (10)

where L_(i) is the amount of movement of an i-th lens group from thewide-angle end to the telephoto end and f_(B(min)) is the length, ascalculated on an air basis, of the final surface of a lens having powerin said zoom lens system to an image plane of said zoom lens system,representing a figure at which said zoom lens system becomes shortest ina whole zooming space.

According to yet another aspect of the present invention, there isprovided a zoom lens system characterized by comprising, in order froman object side of the zoom lens system, a first lens group havingpositive refracting power and designed to be fixed during zooming, asecond lens group having negative refracting power and designed to movefrom the object side to an image plane side of the zoom lens system forzooming from a wide-angle end to a telephoto end of the zoom lenssystem, a third lens group having positive refracting power and designedto move from the object side to the image plane side for zooming fromthe wide-angle end to the telephoto end, and a fourth lens group havingpositive refracting power and designed to be movable for zooming,wherein the following conditions are satisfied:

2<(F _(3.4) w)/IH<3.3  (3)

2.5 mm<f _(B(min))<4.8 mm  (10)

where (F_(3.4W)) is the composite focal length of the third and forthlens groups at the wide-angle end, IH is the radius of an image circle,and f_(B(min)) is the length, as calculated on an air basis, of thefinal surface of a lens having power in said zoom lens system to animage plane of said zoom lens system, representing a figure at whichsaid zoom lens system becomes shortest in a whole zooming space.

According to a further aspect of the present invention, there isprovided a zoom lens system, characterized by comprising, in order froman object side of the zoom lens system, a first lens group havingpositive refracting power, a second lens group having negativerefracting power and designed to move from the object side to an imageplane side of the zoom lens system for zooming a wide-angle end to atelephoto end of the zoom lens system, a third lens group havingpositive refracting power and a fourth lens group having positiverefracting power and designed to be movable for zooming, wherein saidthird lens group comprises, in order from an object side thereof, apositive lens component convex on an object side thereof and a cementedlens consisting of a positive lens element convex on an object sidethereof and a negative lens element concave on an image plane sidethereof, and both the object-side positive lens component and cementedlens in said third lens group are held in a lens barrel while theobject-side convex surfaces thereof abut at their peripheries or theirperipheral spots against said lens barrel, wherein the followingcondition is satisfied:

 2.5 mm<f _(B(min))<4.8 mm  (10)

where f_(B(min)) is the length, as calculated on an air basis, of thefinal surface of a lens having power in said zoom lens system to animage plane of said zoom lens system, representing a figure at whichsaid zoom lens system becomes shortest in a whole zooming space.

Why the aforesaid lens arrangements are herein used and how they workare now explained.

In recent fields of camcorders and digital cameras as well asinformation systems using image pickup devices, e.g., portabletelephones and personal computers, too, there are growing demands forconsumer-oriented compact yet low-cost zoom lenses. Zoom lenses capableof meeting such demands, for instance, are disclosed in JP-A's 6-94997and 6-194572 already referred to herein. As already explained, each zoomlens system has a zoom ratio of about 8 to 12, with a substantialportion of its zooming function allocated to the second lens group. Tokeep a substantially constant image point in this case, the transversemagnification of the second lens group must be in the neighborhood of −1in the range from the wide-angle end to the telephoto end of the system.

When further size reductions are intended by making the zoom ratiosmaller than this, however, the amount of movement of the second lensgroup can be so reduced that the space margin between the first andsecond lens groups can be cut to the bone, thereby achieving efficientsize reductions.

To perform zooming while the second lens group has a transversemagnification in the neighborhood of −1 with a narrower spacing betweenthe first and second lens groups, however, it is required to increasethe power of the first lens group with respect to the second lens group.This in turn causes an entrance pupil to be located at a fartherposition and so the height of off-axis rays passing through the firstlens group to increase, resulting unavoidably in an increase in the sizeand, hence, the thickness of the first lens group. It is also requiredto increase the curvature of each lens in the first lens group. Toensure each lens of sufficient edge thickness, it is then necessary toincrease the thickness of each lens in the first lens group.

According to the present invention, these problems can be averted byincreasing the proportion of the zooming action allocated to the thirdlens group, thereby ensuring the desired zoom ratio with no significantvariation in the power ratio between the first lens group and the secondlens group and, hence, achieving size reductions. To allow the thirdlens group to have such an increased zooming action, it is required tohave relatively large power, as defined by condition (1). When the lowerlimit of 0.5 to condition (1) is not reached or when the power of thethird lens group becomes weak with respect to the power of the secondlens group, no size reductions are achievable because the amount ofzooming movement of the third lens group becomes too large and,accordingly, the amount of movement of the second lens group to keep theimage plane at a constant position becomes large. When the upper limitof 1.2 to condition (1) is exceeded or when the power of the third lensgroup becomes strong with respect to the power of the second lens group,the amount of astigmatism produced at the third lens group becomes toolarge, and no sufficient space can be obtained between the second andthird lens groups because the distance between the third lens group andan object point with respect thereto becomes too short. To insert animage pickup package such as CCDs and CMOSs as well as an IR cut filter,a low-pass filter or the like in the optical system, it is then requiredthat the back focus f_(B) be 2.5 mm or greater. When the back focusf_(B) exceeds 4.8 mm, on the other hand, no compactness can be achieved.For this reason, it is required that the following condition (10) besatisfied.

2.5 mm<f _(B(min))<4.8 mm  (10)

where f_(B(min)) is the length, as calculated on an air basis, of thefinal surface of a lens having power in said zoom lens system to animage plane of said zoom lens system, representing a figure at whichsaid zoom lens system becomes shortest in a whole zooming space. By theterm “lens having power” is herein intended a lens whose refractingpower is not zero.

When the lower limit of 2.5 mm to condition (1) is not reached, it isimpossible to obtain any space for receiving filters such as an IR cutfilter. When the upper limit of 4.5 mm is exceeded, on the other hand,the size of the zoom lens system increases. This condition isparticularly important for reducing the size of an optical system usedwith an image pickup device for portable telephones or notebook PCs.

More preferably, the zoom lens system of the invention should satisfythe following condition (4):

0.6<|F ₂ /F ₃|<1  (4)

To allow the third lens group to have a relatively large zooming actionas mentioned above, it is required to increase the amount of zoomingmovement of the third lens group, as defined by condition (2) giving adefinition of the ratio of the amount of movement from the wide-angleend to the telephoto end between the second lens group and the thirdlens group. When the lower limit of 0.49 to condition (2) is not reachedor when the amount of movement of the third lens group becomes smallwith respect to the second lens group, it is impossible to allocate anysufficient zooming action to the third lens group. When the upper limitof 1 is exceeded or when the amount of movement of the third lens groupbecomes large with respect to the second lens group, fluctuations ofaberrations such as astigmatism and coma become too large during zoomingwith the third lens group, and no sufficient space can be obtainedbetween the second lens group and the third lens group, because thedistance at the telephoto end between the third lens group and theobject point with respect thereto becomes too short.

To reduce the overall length of such a four-group zoom lens system of+−++construction as intended herein, it is effective to make strong thepowers of the third and fourth lens groups for relaying a virtual imageformed by the first and second lens group to the image pickup plane,thereby reducing the distance from the position of the virtual imageformed by the first and second lens groups to the image pickup plane. Itis thus preferable to make the composite power of the third and fourthlens groups strong, as defined by condition (3). When the upper limit of3.3 to condition 3 is exceeded or when the composite focal length of thethird and fourth lens groups at the wide-angle end becomes long withrespect to the image circle radius (image height) IH (the power becomesweak), no sufficient size reductions are achievable for the foregoingreasons. When the lower limit of 2 to condition (3) is not reached orwhen the composite focal length of the third and fourth lens groups atthe wide-angle end becomes short with respect to the image circle radius(the power becomes strong), astigmatisms produced at the third andfourth lens groups become too large, and no sufficient space can beobtained between the second and third lens groups at the telephoto end,because the distance between the third lens group and the object pointwith respect thereto becomes too short.

For such a zoom lens system as intended herein, it is preferable tocarry out focusing with the fourth lens group wherein the angle ofincidence of an axial light beam is relatively small, because aberrationfluctuations with focusing can be limited. In addition, the fourth lensgroup, because of being relatively small in lens diameter and light inweight, has the merit of reducing the driving torque for focusing.

To reduce the overall length of the zoom lens system, the largestpossible portion of the composite power of the third and fourth lensgroups should preferably be allocated to the third lens group. In thepresent invention, the power of the third lens group is thus relativelylarger than that of the fourth lens group, as defined by the followingcondition (5) giving a definition of the ratio of the focal length ofthe third lens group with respect to that of the fourth lens group.

0.3<F ₃ /F ₄<0.8  (5)

Here F_(i) is the focal length of an i-th lens group. By making thefocal length ratio of the third lens group with respect to the fourthlens group lower than the upper limit of 0.8 to condition (5), it ispossible to achieve more considerable size reductions than ever before.When the focal length ratio of the third lens group with respect to thefourth lens group is below the lower limit of 0.3 to condition 5,however, the power of the fourth lens group becomes too weak or theamount of focusing movement of the fourth lens group becomes too large,resulting in increased aberration fluctuations with focusing.

To reduce the size of the zoom lens system according to the presentinvention, the fourth lens group should preferably comprise one positivelens. This is because the power of the fourth lens group is relativelysmaller than that of the third lens group, as mentioned above.

To reduce astigmatism fluctuations with zooming, at least one surface inthe fourth lens group should preferably be defined by an asphericalsurface.

Preferably, the zoom lens system of the present invention should satisfythe following condition (6):

0.4<|β_(2T)|<1  (6)

Here β_(2T) is the transverse magnification of the second lens group atthe telephoto end of the zoom lens system.

Condition (6) gives a definition of the absolute value of the transversemagnification of the second lens group at the telephoto end of the zoomlens system. When the absolute value of the transverse magnification ofthe second lens group at the telephoto end is below the lower limit of0.4, the zooming action of the second lens group becomes insufficientand the power of the first lens group becomes too weak to achieve lenssize reductions. On the other hand, when the absolute value of thetransverse magnification of the second lens group at the telephoto endexceeds the upper limit of 1, the zooming action of the third lens groupbecomes insufficient and the power of the first lens group becomes toostrong, resulting in an increase in the lens diameter of the first lensgroup and failing to achieve size reductions.

To reduce the overall size of the zoom lens system, the third lens groupshould preferably have an increased power with no change in itsimage-formation magnification. Preferably in this case, the principalpoints of the third lens group should be positioned as close to theobject side as possible, thereby preventing the interference of thesecond lens group with the third lens group at the telephoto end, whichmay otherwise be caused by a reduction in the distance between the thirdlens group and the object point with respect to the third lens group.Thus, the third lens group should comprise three lenses or a positive, apositive and a negative lens in order from the object side, with atleast one aspherical surface provided for correction of sphericalaberrations.

If at least one surface in the second lens group is defined by anaspherical surface, it is then possible to make much better correctionfor fluctuations of astigmatism and coma with zooming.

In the present invention, the relatively large zooming action isassigned to the third lens group as mentioned above, so that loads ofcorrection of aberrations on the first and second lens groups can berelieved. For this reason, the first lens group can be comprised of onepositive lens. To make correction for chromatic aberration ofmagnification produced at the first lens group, the lens located nearestto the object side in the second lens group should preferably becomposed of a negative lens having relatively large dispersion, asdefined by the following condition (7) giving a definition of the Abbe'snumber of the negative lens located nearest to the object side in thesecond lens group.

ν₂₁<40  (7)

Here ν₂₁ is the Abbe's number of the negative lens located nearest tothe object side in the second lens group.

To make correction for the chromatic aberration of magnificationproduced at the first lens group or the positive lens, it is preferablethat the Abbe's number of the negative lens located nearest to theobject side in the second lens group does not exceed the upper limit of40 to condition (7). If the following condition (8) is satisfied, it isthen possible to make much better correction for the chromaticaberration of magnification.

ν₂₁<35  (8)

When the third lens group is made up of three lenses or a positive, apositive and a negative lens in order from the object side ascontemplated herein, two positive lenses should be each convex on anobject side thereof and one negative lens should have a strong concavesurface on an image plane side thereof. This is because the principalpoints of the third lens groups should be located as close to the objectside as possible for the purpose of size reductions. Two such positivelenses having strong refracting power and convex surfaces on theirobject sides and such a negative lens having a concave surface on itsimage plane side, if they are fabricated with decentration errors withrespect to their optical axes, have increased influences ondeterioration of performance. For this reason, the positive lens on theimage plane side and the negative lens should preferably be cementedtogether. When this cemented lens and the positive lens on the objectside are held in a lens holder, it is preferable that they are receivedtherein while the peripheral edges of the convex surfaces thereof abutat their peripheries or at their peripheral several spots against thelens holder.

According to a further embodiment of the present invention, there isprovided a zoom lens system characterized by comprising, in order froman object side of said zoom lens system, a first lens group havingpositive refracting power and designed to be fixed during zooming, asecond lens group having negative refracting power and designed to movefrom the object side to an image plane side of said zoom lens system forzooming from a wide-angle end to a telephoto end of said zoom lenssystem, a third lens group having positive refracting power and designedto move constantly from the image plane side to the object side forzooming from the wide-angle end to the telephoto end, and a fourth lensgroup having positive refracting power and designed to be movable duringzooming, wherein said third lens group comprises a cemented lensconsisting of a positive lens and a negative lens, said fourth lensgroup comprises one positive lens, and the following condition (10) issatisfied.

2.5 mm<f _(B(min))<4.8 mm  (10)

For zooming from the wide-angle end to the telephoto end according tothis arrangement, the second lens group having negative refracting poweris moved from the object side to the image plane side and the third lensgroup having positive refracting power is moved from the image planeside to the object side, so that the zooming load so far applied on thesecond lens group can be assigned to the second and third lens groups.This in turn makes it possible to obtain the desired zoom ratio andachieve size reductions without increasing the power ratio of the firstlens group with respect to the second lens group. According to such anarrangement wherein the proportion of the zooming action allocated tothe third lens group is increased, it is thus possible to obtain thedesired zoom ratio and achieve size reductions without increasing thepower ratio of the first lens group with the second lens group.

Reference is now made to what action and effect are obtained when thethird lens group comprises a cemented lens consisting of a positive lensand a negative lens. When the third lens group is designed to be movableduring zooming, the load of correction of aberration fluctuations withzooming on the third lens group increases with the need of making moresatisfactory correction for chromatic aberrations. For this reason, thethird lens group is required to comprise a positive lens component and anegative lens component. If, in this case, relative decentration occursbetween the positive lens and the negative lens, there is then largedeterioration of image-formation capability. In the aforesaidarrangement, the decentration between the positive lens and the negativelens can be easily reduced by using a cemented lens consisting of apositive lens and a negative lens in the third lens group. In otherwords, it is possible to increase the proportion of the zooming actionassigned to the third lens group, make good correction for chromaticaberrations, and make image quality unlikely to deteriorate due todecentration.

According to the aforesaid arrangement wherein the load of zooming sofar assigned to the second lens group is allocated to the second andthird lens groups, the load of correction of aberrations on the fourthlens group can be successfully reduced, so that the fourth lens groupcan be constructed of one positive lens and, hence, the desiredimage-formation capability can be obtained with size reductions.

In the aforesaid arrangement, it is preferable that at least one surfaceof the positive lens forming the fourth lens group is defined by anaspherical surface.

When the fourth lens group is constructed of one positive lens togetherwith one aspherical surface introduced therein, the load of zooming canbe allocated to the second and third lens groups, and the fourth lensgroup—whose weight is reduced accordingly—makes it possible to achievemuch better correction for aberrations, resulting in further cost andsize reductions. It is noted that the aspherical surface used here maybe formed by a so-called glass pressing process, a (so-called hybrid)process for applying a thin resin layer on a glass or other substrate,or a plastic molding process.

According to a further embodiment of the present invention, there isprovided a zoom lens system characterized by comprising, in order froman object side of said zoom lens system, a first lens group havingpositive refracting power and designed to be fixed during zooming, asecond lens group having negative refracting power and designed to movefrom the object side to an image plane side of said zoom lens system forzooming from a wide-angle end to a telephoto end of said zoom lenssystem, a third lens group having positive refracting power and designedto move constantly from the image plane side to the object side forzooming from the wide-angle end to the telephoto end, and a fourth lensgroup having positive refracting power and designed to be movable duringzooming, wherein said second lens group, and said third lens groupcomprises a cemented lens consisting of a positive lens and a negativelens, and the following condition (10) is satisfied.

2.5 mm<f _(B(min))<4.8 mm  (10)

For zooming from the wide-angle end to the telephoto end according tothis arrangement, the second lens group having negative refracting poweris moved from the object side to the image plane side and the third lensgroup having positive refracting power is moved from the image planeside to the object side, so that the zooming load so far applied on thesecond lens group can be assigned to the second and third lens groups.This in turn makes it possible to obtain the desired zoom ratio andachieve size reductions without increasing the power ratio of the firstlens group with respect to the second lens group. According to such anarrangement wherein the proportion of the zooming action allocated tothe third lens group is increased, it is thus possible to obtain thedesired zoom ratio and achieve size reductions without increasing thepower ratio of the first lens group with the second lens group.

Reference is now made to what action and effect are obtained when thethird lens group comprises a cemented lens consisting of a positive lensand a negative lens. When the third lens group is designed to be movableduring zooming, the load of correction of aberration fluctuations withzooming on the third lens group increases with the need of making moresatisfactory correction for chromatic aberrations. For this reason, thethird lens group is required to comprise a positive lens component and anegative lens component. If, in this case, relative decentration occursbetween the positive lens and the negative lens, there is then largedeterioration of image-formation capability. In the aforesaidarrangement, the decentration between the positive lens and the negativelens can be easily reduced by using a cemented lens consisting of apositive lens and a negative lens in the third lens group. In otherwords, it is possible to increase the proportion of the zooming actionassigned to the third lens group, make good correction for chromaticaberrations, and make deterioration of image quality due to decentrationunlikely to occur.

Although the load applied on the second lens group is reduced, this lensgroup is a movable lens group during zooming. Still, a large load isimposed on the second lens group to make correction for aberrationfluctuations with zooming; it is required to make satisfactorycorrection for chromatic aberrations. It is thus required that thesecond lens group comprise at least a positive lens component and anegative lens component. When, at this time, relative decentrationoccurs between the positive lens and the negative lens, theimage-formation capability deteriorates excessively. According to theaforesaid arrangement wherein a cemented lens consisting of a positivelens and a negative lens is introduced in the second lens group, thedecentration between the positive lens and the negative lens can beeasily reduced. It is thus possible to make deterioration of imagequality due to unlikely to occur.

According to a further embodiment of the present invention, there isprovided a zoom lens system characterized by comprising, in order froman object side of said zoom lens system, a first lens group havingpositive refracting power and designed to be fixed during zooming, asecond lens group having negative refracting power and designed to movefrom the object side to an image plane side of said zoom lens system forzooming from a wide-angle end to a telephoto end of said zoom lenssystem, a third lens group having positive refracting power and designedto move constantly from the image plane side to the object side forzooming from the wide-angle end to the telephoto end, and a fourth lensgroup having positive refracting power and designed to be movable duringzooming, wherein said third lens group comprises, in order from anobject side thereof, a positive lens and a cemented lens consisting of apositive lens and a negative lens, and the following condition (10) issatisfied.

2.5 mm<f _(B(min))<4.8 mm  (10)

For zooming from the wide-angle end to the telephoto end according tothis arrangement, the second lens group having negative refracting poweris moved from the object side to the image plane side and the third lensgroup having positive refracting power is moved from the image planeside to the object side, so that the zooming load so far applied on thesecond lens group can be assigned to the second and third lens groups.This in turn makes it possible to obtain the desired zoom ratio andachieve size reductions without increasing the power ratio of the firstlens group with respect to the second lens group. According to such anarrangement wherein the proportion of the zooming action allocated tothe third lens group is increased, it is thus possible to obtain thedesired zoom ratio and achieve size reductions without increasing thepower ratio of the first lens group with the second lens group.

The third lens group is constructed of three lenses or a positive, apositive and a negative lens in order from an object side thereof, sothat the principal points of the third lens group can be generallylocated to the object side, thereby achieving further size reductions.Here, the negative lens is needed for correction of chromaticaberrations, and two positive lenses are needed to obtain strongpositive power and reduce the size of the third lens group itself(simplify the construction of the third lens group itself). The ++−construction of the third lens group in order from the object side alsoallows various aberrations to be well corrected with a reduced number oflenses and the principal points of the third lens group to be generallylocated on the object side, so that the principal point positions of thesecond and third lens groups can efficiently be brought close to eachother at the telephoto end, thereby achieving further size reductions ofthe zoom lens system.

According to a further embodiment of the present invention, there isprovided a zoom lens system characterized by comprising, in order froman object side of said zoom lens, a first lens group having positiverefracting power, a second lens group having negative refracting power,a third lens group having positive refracting power and a fourth lensgroup having positive refracting power, wherein a spacing between saidfirst lens group and said second lens group, a spacing between saidsecond lens group and said third lens group, and a spacing between saidthird lens group and said fourth lens group varies upon zooming, saidthird lens group comprises, in order from an object side thereof, adouble-convex positive lens and a cemented lens consisting of a positivemeniscus lens convex on an object side thereof and a negative meniscuslens, said fourth lens group comprises a double-convex lens in which anobject-side surface thereof has a larger curvature, and the followingcondition (10) is satisfied.

2.5 mm<f _(B(min))<4.8 mm  (10)

According to this arrangement wherein the third lens group comprises, inorder from an object side thereof, a positive lens convex on an objectside thereof and a cemented lens consisting of a positive meniscus lensconvex on an object side thereof and a negative meniscus lens, theprincipal points of the third lens group can generally be located on theobject side, so that the size of the zoom lens system can be reduced.The cemented lens consisting of a positive meniscus lens and a negativemeniscus lens is effective to reduce deterioration of performance due todecentration. The third lens group of such construction enables thefourth lens group to be made up one single lens. By using as the singlelens a double-convex lens wherein an object-side surface thereof has alarger curvature, it is further possible to make light rays incident onan image plane nearly telecentric and obtain the desired back focuswhile the number of lenses in the fourth lens group is minimized. It isthus possible to accomplish the aforesaid another object of the presentinvention.

According to a further embodiment of the present invention, there isprovided a zoom lens system characterized by comprising, in order froman object side of said zoom lens, a first lens group having positiverefracting power, a second lens group having negative refracting power,a third lens group having positive refracting power and a fourth lensgroup having positive refracting power, wherein a spacing between saidfirst lens group and said second lens group, a spacing between saidsecond lens group and said third lens group, and a spacing between saidthird lens group and said fourth lens group varies upon zooming, saidthird lens group comprises three lenses or a single lens and a cementedlens consisting of a positive lens and a negative lens in order from anobject side thereof, said fourth lens group comprises one positive lens,and the following condition (10) is satisfied.

2.5 mm<f _(B(min))<4.8 mm  (10)

According to this arrangement, it is possible to achieve a zoom lenssystem of +−++ construction, which ensures satisfactory image-formationcapability with a reduced number of lenses and is suitable for use ondigital cameras. Here, the load of correction of aberrations is assignedexclusively to the second and third lens groups, and so the first andfourth lens groups taking less part in correction of aberrations can beeach composed of one positive lens. According to the construction of thesecond lens group taking a substantial part in correction of aberrationswherein a single lens and a cemented lens consisting of a negative lensand a positive lens are provided in order from the object side, it ispossible to reduce with a minimum number of lenses various aberrationsinclusive of chromatic aberration produced at the third lens groupalone, thereby making an additional contribution to size reductions. Thecemented lens consisting of a negative lens and a positive lens,introduced in the third lens group, makes it possible to reducedeterioration of performance due to decentration.

Preferably, the power of the first lens group should be decreased,because the amount of aberrations produced at the first lens group canbe reduced so that the load of correction of aberrations produced at thefirst lens group on the second and third lens groups can be reduced.Preferably, the zoom lens system according to this embodiment shouldsatisfy the following condition (9):

8<F ₁ /IH<20  (9)

Here F₁ is the focal length of the first lens group, and IH representsan image height (the length from the center of an image to the peripheryof the image or the radius of an image circle). Falling below the lowerlimit of 8 to condition (9) is not preferable because the amount ofaberrations produced at the first lens group becomes large. When theupper limit of 20 is exceeded, the power of the first lens group becomestoo weak to obtain the desired sufficient zoom ratio or achieve sizereductions.

According to a further embodiment of the present invention, there isprovided a zoom lens system characterized by comprising, in order froman object side of said zoom lens, a first lens group having positiverefracting power, a second lens group having negative refracting power,a third lens group having positive refracting power and a fourth lensgroup having positive refracting power, wherein a spacing between saidfirst lens group and said second lens group, a spacing between saidsecond lens group and said third lens group, and a spacing between saidthird lens group and said fourth lens group varies upon zooming, saidfirst lens group comprises two lenses or a positive lens and a negativelens, said second or third lens group includes therein a cemented lensconsisting of at least one set of a positive lens and a negative lens,and the following condition (10) is satisfied.

2.5 mm<f _(B(min))<4.8 mm  (10)

According to this arrangement wherein the first lens group comprises twolenses or a positive lens and a negative lens, chromatic aberrationproduced at the first lens group can be reduced irrespective of thepower of the first lens group, so that the load of correction ofchromatic aberrations on the second, third, and fourth lens groups canbe relieved to reduce the overall size of the zoom lens system. Byintroducing the cemented lens consisting of a positive lens and anegative lens in the second or third lens group, it is then possible toreduce chromatic aberrations produced at lens groups other than thefirst lens group and prevent deterioration of image-formation capabilitydue to decentration, etc. It is thus possible to achieve an opticalsystem that is favorable in view of the number of lenses, fabricationcost, and size.

Preferably, the zoom lens systems according to the aforesaid embodimentsof the present invention should satisfy the following condition (11).

2.5 mm<f _(B(max))<4.8 mm  (11)

Here f_(B(max)) is the length, as calculated on an air basis, of thefinal surface of a lens having power in said zoom lens system to animage plane of said zoom lens system, representing a figure at whichsaid zoom lens system becomes longest in a whole zooming space.

When the lower limit of 2.5 mm to condition (11) is not reached, it isimpossible to obtain any space for receiving image pickup devicepackages or filters such as IR cut filters and low-pass filters, as inthe case of condition

(10). Accordingly, when these packages or filters are incorporated inthe optical system, interference or other problems are likely to arise.When the upper limit of 4.8 mm is exceeded, on the other hand, no sizereductions are achievable. This condition is important to conform zoomlens system size to the size of portable information terminals such asportable telephones and notebook PCs, in which the zoom lens system isincorporated.

For further size reductions, it is more preferable that

2.5 mm<f _(B(min))<4.0 mm

For further size reductions, it is more preferable that

2.5 mm<f _(B(max))<4.0 mm

Still other objects and advantages of the present invention will in partbe obvious and will in part be apparent from the specification.

The present invention accordingly comprises the features ofconstruction, combinations of elements, and arrangement of parts whichwill be exemplified in the construction hereinafter set forth, and thescope of the present invention will be indicated in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional schematic illustrative of Example 1 of the zoomlens system according to the present invention, as viewed at thewide-angle end.

FIG. 2 is a sectional schematic illustrative of Example 2 of the zoomlens system according to the present invention, as viewed at thewide-angle end.

FIG. 3 is a sectional schematic illustrative of Example 3 of the zoomlens system according to the present invention, as viewed at thewide-angle end.

FIG. 4 is a sectional schematic illustrative of Example 4 of the zoomlens system according to the present invention, as viewed at thewide-angle end.

FIG. 5 is a sectional schematic illustrative of Example 5 of the zoomlens system according to the present invention, as viewed at thewide-angle end.

FIG. 6 is a sectional schematic illustrative of Example 6 of the zoomlens system according to the present invention, as viewed at thewide-angle end.

FIG. 7 is a sectional schematic illustrative of Example 7 of the zoomlens system according to the present invention, as viewed at thewide-angle end.

FIG. 8 is a sectional schematic illustrative of Example 8 of the zoomlens system according to the present invention, as viewed at thewide-angle end.

FIG. 9 is a sectional schematic illustrative of Example 9 of the zoomlens system according to the present invention, as viewed at thewide-angle end.

FIG. 10 is a sectional schematic illustrative of Example 10 of the zoomlens system according to the present invention, as viewed at thewide-angle end.

FIG. 11 is illustrative of a holding structure for the third lens groupin Example 5.

FIG. 12 is an aberration diagram for Example 1 at the wide-angle end.

FIG. 13 is an aberration diagram for Example 1 at the telephoto end.

FIG. 14 is a front perspective view illustrative of the appearance of anelectronic camera wherein the zoom lens system of the present inventionis incorporated in the form of an objective optical system.

FIG. 15 is a rear perspective view illustrative of the electronic camerawherein the zoom lens system of the present invention is incorporated inthe form of an objective optical system.

FIG. 16 is a sectional view illustrative of the electronic camerawherein the zoom lens system of the present invention is incorporated inthe form of an objective optical system.

FIG. 17 is a front perspective view illustrative of an uncoveredpersonal computer wherein the zoom lens system of the present inventionis incorporated in the form of an objective optical system.

FIG. 18 is a sectional view of a phototaking optical system in thepersonal computer.

FIG. 19 is a side view of FIG. 17.

FIGS. 20(a) and 20(b) are a front and a side view illustrative of aportable telephone wherein the zoom lens system of the present inventionis incorporated in the form of an objective optical system, and FIG.20(c) is a sectional view of a phototaking optical system.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Examples 1 to 10 of the zoom lens system according to the presentinvention are now explained.

FIGS. 1 through 10 are sectional views, as viewed at the wide-angleends, of Examples 1 to 10 of the zoom lens system according to thepresent invention. Numerical data on each example will be set out later.Throughout the embodiments shown in FIGS. 1 to 10, plane-parallel platesare located between the fourth lens groups G4 and image planes. These,for instance, include an image pickup device cover glass, and filterssuch as an IR cut filter and a low-pass filter. These plane-parallelplates are omitted from the numerical data given later.

Example 1 is directed to a zoom lens system having a focal length of3.643 to 10.420 mm and a field angle of 66.42° to 24°. As shown in FIG.1, the first lens group G1 is made up of a cemented lens consisting of anegative meniscus lens convex on an object side thereof and adouble-convex lens and a positive meniscus lens convex on an object sidethereof. The second lens group G2 is made up of a negative meniscus lensconvex on an object side thereof and a cemented lens consisting of adouble-concave lens and a double-convex lens. In the rear of the secondlens group G2 there is located a stop S. The third lens group G3 is madeup of two double-convex lenses and a negative meniscus lens convex on anobject side thereof, and the fourth lens group G4 is made up of onepositive meniscus lens convex on an object side thereof. One aspehricalsurface is used for the surface located nearest to the object side inthe third lens group G3. For zooming from the wide-angle end to thetelephoto end, the first lens group G1 and the stop S remain fixed, thesecond lens group G2 moves from the object side to the image plane side,and the third and fourth lens groups G3 and G4 move from the image planeside to the object side while the space therebetween becomes wide, asindicated by arrows.

Example 2 is directed to a zoom lens system having a focal length of2.924 to 8.425 mm and a field angle of 67.04° to 23.72°. As shown inFIG. 2, the first lens group G1 is made up of a cemented lens consistingof a negative meniscus lens convex on an object side thereof and apositive meniscus lens, and the second lens group G2 is made up of anegative meniscus lens convex on an object side thereof, adouble-concave lens and a positive meniscus lens convex on an objectside thereof. In the rear of the second lens group G1 there is located astop S. The third lens group G3 is made up of two double-convex lensesand a negative meniscus lens convex on an object side thereof, and thefourth lens group G4 is made up of one double-convex lens. Oneaspehrical surface is used for the surface located nearest to the objectside in the third lens group G3. For zooming from the wide-angle end tothe telephoto end, the first lens group G1 and the stop S remain fixed,the second lens group G2 moves from the object side to the image planeside, and the third and fourth lens groups G3 and G4 move from the imageplane side to the object side while the space therebetween becomes wide,as indicated by arrows.

Example 3 is directed to a zoom lens system having a focal length of3.238 to 9.300 mm and a field angle of 66.82° to 23.88°. As shown inFIG. 3, the first lens group G1 is made up of a cemented lens consistingof a negative meniscus lens convex on an object side thereof and adouble-convex lens, and the second lens group G2 is made up of adouble-concave lens and a positive lens. In the rear of the second lensgroup G2 there is located a stop S. The third lens group G3 is made upof a double-convex lens, a positive meniscus lens convex on an objectside thereof and a negative meniscus lens convex on an object sidethereof, and the fourth lens group G4 is made up of one positivemeniscus lens convex on an object side thereof. Three asphericalsurfaces are used; one for the surface located nearest to the imageplane side in the second lens group G2, one for the surface locatednearest to the object side in the third lens group G3 and one for thesurface located nearest to the object side in the fourth lens group G4.For zooming from the wide-angle end to the telephoto end, the first lensgroup G1 and the stop S remain fixed, the second lens group G2 movesfrom the object side to the image plane side, and the third and fourthlens groups G3 and G4 move from the image plane side to the object sidewhile the space therebetween becomes wide, as indicated by arrows.

Example 4 is directed to a zoom lens system having a focal length of3.144 to 9.070 mm and a field angle of 64.93° to 24.87°. As shown inFIG. 4, the first lens group G1 is made up of one positive meniscus lensconvex on an object side thereof, and the second lens group G2 is madeup of a negative meniscus lens convex on an object side thereof and acemented lens consisting of a double-concave lens and a positivemeniscus lens convex on an object side thereof. In the rear of thesecond lens group G2 there is located a stop S. The third lens group G3is made up of a double-convex lens and a cemented lens consisting of apositive meniscus lens convex on an object side thereof and a negativemeniscus lens, and the fourth lens group G4 is made up of onedouble-convex lens. Two aspherical surfaces are used; one for thesurface located nearest to the object side in the third lens group G3and another for the surface located nearest to the object side in thefourth lens group G4. For zooming from the wide-angle end to thetelephoto end, the first lens group G1 and the stop S remain fixed, thesecond lens group G2 moves from the object side to the image plane side,and the third and fourth lens groups G3 and G4 move from the image planeside to the object side while the space therebetween becomes wide, asindicated by arrows.

Example 5 is directed to a zoom lens system having a focal length of3.578 to 10.193 mm and a field angle of 68.30° to 24.54°. As shown inFIG. 5, the first lens group G1 is made up of a negative meniscus lensconvex on an object side thereof and a positive meniscus lens convex onan object side thereof, and the second lens group G2 is made up of anegative meniscus lens convex on an object side thereof and a cementedlens consisting of a double-concave lens and a positive meniscus lensconvex on an object side thereof. In the rear of the second lens groupG2 there is located a stop S. The third lens group G3 is made up of adouble-convex lens and a cemented lens consisting of a positive meniscuslens convex on an object side thereof and a negative meniscus lensconvex on an object side thereof, and the fourth lens group G4 is madeup of one double-convex lens. Three aspherical surfaces are used; onefor the surface located nearest to the image plane side in the secondlens group G2, one for the surface located nearest to the object side inthe third lens group G3 and one for the surface located nearest to theobject side in the fourth lens group G4. For zooming from the wide-angleend to the telephoto end, the first lens group G1 and the stop S remainfixed, the second lens group G2 moves from the object side to the imageplane side, and the third and fourth lens groups G3 and G4 move from theimage plane side to the object side while the space therebetween becomeswide, as indicated by arrows.

In Example 5, it is noted that both the object-side positive lens L₃₁and cemented lens L₃₂ in the third lens group G3 are held while theperipheral edges of the convex surfaces thereof abut peripherally or atseveral spots against a lens holder 1, so that decentration errorslikely to have an influence on performance can be reduced.

Example 6 is directed to a zoom lens system having a focal length of2.478 to 7.162 mm and a field angle of 67.32° to 25.95°. As shown inFIG. 6, the first lens group G1 is made up of one plano-convex lens, andthe second lens group G2 is made up of a negative meniscus lens convexon an object side thereof and a cemented lens consisting of adouble-concave lens and a positive meniscus lens convex on an objectside thereof. In the rear of the second lens group G2 there is located astop S. The third lens group G3 is made up of a double-convex lens and acemented lens consisting of a positive meniscus lens convex on an objectside thereof and a negative meniscus lens convex on an object sidethereof, and the fourth lens group G4 is made up of one double-convexlens. Two aspherical surfaces are used; one for the surface locatednearest to the object side in the third lens group G3 and another forthe surface located nearest to the object side in the fourth lens groupG4. For zooming from the wide-angle end to the telephoto end, the firstlens group G1 and the stop S remain fixed, the second lens group G2moves from the object side to the image plane side, and the third andfourth lens groups G3 and G4 move from the image plane side to theobject side while the space therebetween becomes wide, as indicated byarrows.

Example 7 is directed to a zoom lens system having a focal length of2.976 to 8.549 mm and a field angle of 67.68° to 26.08°. As shown inFIG. 7, the first lens group G1 is made up of one plano-convex lens, andthe second lens group G2 is made up of a negative meniscus lens convexon an object side thereof and a cemented lens consisting of adouble-concave lens and a positive meniscus lens convex on an objectside thereof. In the rear of the second lens group G2 there is located astop S. The third lens group G3 is made up of a double-convex lens and acemented lens consisting of a positive meniscus lens convex on an objectside thereof and a negative meniscus lens convex on an object sidethereof, and the fourth lens group G4 is made up of a double-convex lensand a negative meniscus lens convex on an image plane side thereof. Oneaspehrical surface is used for the surface located nearest to the objectside in the third lens group G3. For zooming from the wide-angle end tothe telephoto end, the first lens group G1 and the stop S remain fixed,the second lens group G2 moves from the object side to the image planeside, and the third and fourth lens groups G3 and G4 move from the imageplane side to the object side while the space therebetween becomes wide,as indicated by arrows.

Example 8 is directed to a zoom lens system having a focal length of4.093 to 11.875 mm and a field angle of 67.80° to 26.08°. As shown inFIG. 8, the first lens group G1 is made up of a negative meniscus lensconvex on an object side thereof and a positive meniscus lens convex onan object side thereof, and the second lens group G2 is made up of anegative meniscus lens convex on an object side thereof and a cementedlens consisting of a double-concave lens and a positive meniscus lensconvex on an object side thereof. In the rear of the second lens groupG2 there is located a stop S. The third lens group G3 is made up of adouble-convex lens and a cemented lens consisting of a double-convexlens and a double-concave lens, and the fourth lens group is made up ofone double-convex lens. Two aspherical surfaces are used; one for thesurface located nearest to the object side in the third lens group G3and another for the surface located nearest to the object side in thefourth lens group G4. For zooming from the wide-angle end to thetelephoto end, the first lens group G1 and the stop S remain fixed, thesecond lens group G2 moves from the object side to the image plane side,and the third and fourth lens groups G3 and G4 move from the image planeside to the object side while the space therebetween becomes wide, asindicated by arrows.

Example 9 is directed to a zoom lens system having a focal length of3.281 to 9.500 mm and a field angle of 67.69° to 26.08°. As shown inFIG. 9, the first lens group G1 is made up of a cemented lens consistingof a negative meniscus lens convex on an object side thereof and apositive meniscus lens convex on an object side thereof, and the secondlens group G2 is made up of a negative meniscus lens convex on an objectside thereof and a cemented lens consisting of a double-concave lens anda positive meniscus lens convex on an object side thereof. In the rearof the second lens group G2 there is located a stop S. The third lensgroup G3 is made up of a double-convex lens and a cemented lensconsisting of a double-convex lens and a double-concave lens, and thefourth lens group G4 is made up of one double-convex lens. Twoaspherical surfaces are used; one for the surface located nearest to theobject side in the third lens group G3 and another for the surfacelocated nearest to the object side in the fourth lens group G4. Forzooming from the wide-angle end to the telephoto end, the first lensgroup G1 and the stop S remain fixed, the second lens group G2 movesfrom the object side to the image plane side, and the third and fourthlens groups G3 and G4 move from the image plane side to the object sidewhile the space therebetween becomes wide, as indicated by arrows.

Example 10 is directed to a zoom lens system having a focal length of3.634 to 10.687 mm and a field angle of 68.52° to 26.08°. As shown inFIG. 10, the first lens group G1 is made up of a cemented lensconsisting of a negative meniscus lens convex on an object side thereofand a positive meniscus lens convex on an object side thereof, and thesecond lens group G2 is made up of a negative meniscus lens convex on anobject side thereof and a cemented lens consisting of a double-concavelens and a positive meniscus lens convex on an object side thereof. Inthe rear of the second lens group G2 there is located a stop S. Thethird lens group G3 is made up of a double-convex lens and a cementedlens consisting of a double-convex lens and a double-concave lens, andthe fourth lens group G4 is made up of one double-convex lens. Twoaspherical surfaces are used; one for the surface located nearest to theobject side in the third lens group G3 and another for the surfacelocated nearest to the object side in the fourth lens group G4. Forzooming from the wide-angle end to the telephoto end, the first lensgroup G1 and the stop S remain fixed, the second lens group G2 movesfrom the object side to the image plane side, and the third and fourthlens groups G3 and G4 move from the image plane side to the object sidewhile the space therebetween becomes wide, as indicated by arrows.

Set out below are numerical data on each example, with the unit oflength being mm. Symbols used hereinafter but not hereinbefore have thefollowing meanings.

f: the focal length of the zoom lens system,

F_(NO): an F-number,

f_(B): a back focus as calculated on an air basis,

r₁, r₂, . . . : the radius of curvature of each lens surface,

d₁, d₂, . . . : the separation between adjacent lens surfaces,

n_(d1), n_(d2), . . . : the d-line refractive index of each lens, and

ν_(d1), ν_(d2), . . . : the Abbe number of each lens.

Here let x denote an optical axis provided that the direction ofpropagation of light is positive and y represent a directionperpendicular to the optical axis. Then, aspherical shape is given by

x=(y ² /r)/[1+{1−(K+1)(y/r)²}^(½) ]+A ₄ y ⁴ +A ₆ y ⁶ +A ₈ y ⁸ +A ₁₀ y ¹⁰+A ₁₂ y ¹²

where r is the paraxial radius of curvature, K is a conical coefficient,and A₄, A₆, A_(B), A₁₀ and A₁₂ are the fourth, sixth, eighth, tenth andtwelfth aspherical coefficients, respectively.

EXAMPLE 1

f=3.643˜6.310˜10.420

F _(NO)=2.79˜3.22˜4.11

f _(B)=3.43˜3.73˜4.11

r₁ = 123.446 d₁ = 0.79 n_(d1) = 1.84666 ν_(d1) = 23.78 r₂ = 26.028 d₂ =2.63 n_(d2) = 1.48749 ν_(d2) = 70.23 r₃ = −37.648 d₃ = 0.12 r₄ = 9.745d₄ = 2.16 n_(d3) = 1.69680 ν_(d3) = 55.53 r₅ = 41.109 d₅ = (Variable) r₆= 49.306 d₆ = 0.56 n_(d4) = 1.77250 ν_(d4) = 49.60 r₇ = 3.668 d₇ = 1.97r₈ = −6.439 d₈ = 0.56 n_(d5) = 1.48749 ν_(d5) = 70.21 r₉ = 7.824 d₉ =1.19 n_(d6) = 1.84666 ν_(d6) = 23.78 r₁₀ = −92.465 d₁₀ = (Variable) r₁₁= ∞ (Stop) d₁₁ = (Variable) r₁₂ = 7.726 (Aspheric) d₁₂ = 1.29 n_(d7) =1.58913 ν_(d7) = 61.18 r₁₃ = −15.280 d₁₃ = 0.10 r₁₄ = 5.743 d₁₄ = 1.73n_(d8) = 1.72916 ν_(d8) = 54.68 r₁₅ = −8.215 d₁₅ = 0.20 r₁₆ = 17.851 d₁₆= 0.46 n_(d9) = 1.84666 ν_(d9) = 23.78 r₁₇ = 2.797 d₁₇ = (Variable) r₁₈= 6.406 d₁₈ = 1.07 n_(d10) = 1.72916 ν_(d10) = 54.68 r₁₉ = 21.794

Zooming Spaces

f  3.643  6.310 10.420 d₅ 0.64 2.95 4.22 d₁₀ 4.43 2.13 0.86 d₁₁ 3.242.25 0.62 d₁₇ 1.61 2.30 3.55

Aspherical Coefficients

12 th surface

K=−0.218

A ₄=−3.12469×10⁻³

A ₆=−2.00580×10⁻⁴

A ₈2.58848×10⁻⁵

A ₁₀=−3.98934×10⁻⁶

|F ₂ /F ₃|0.714

F ₃ /F ₄−0.539

|β_(2T)|=0.897

|L ₃ /L ₂|=0.73

(F _(3.4) w)/IH=2.44

F ₁ /IH=6.97

IH=2.25

EXAMPLE 2

f=2.924˜5.049˜8.425

F _(NO)=2.78˜3.39˜4.22

f _(B)=2.69˜3.00˜4.18

r₁ = 9.603 d₁ = 0.64 n_(d1) = 1.84666 ν_(d1) = 23.78 r₂ = 6.804 d₂ =2.74 n_(d2) = 1.60311 ν_(d2) = 60.64 r₃ = 121.247 d₃ = (Variable) r₄ =21.867 d₄ = 0.41 n_(d3) = 1.65160 ν_(d3) = 58.55 r₅ = 2.740 d₅ = 1.87 r₆= −17.627 d₆ = 0.37 n_(d4) = 1.56384 ν_(d4) = 60.67 r₇ = 10.992 d₇ =−0.01   r₈ = 4.352 d₈ = 0.93 n_(d5) = 1.80518 ν_(d5) = 25.42 r₉ = 6.985d₉ = (Variable) r₁₀ = ∞ (Stop) d₁₀ = (Variable) r₁₁ = 6.533 (Aspheric)d₁₁ = 1.96 n_(d6) = 1.67790 ν_(d6) = 55.34 r₁₂ = −6.275 d₁₂ = 0.45 r₁₃ =6.079 d₁₃ = 1.25 n_(d7) = 1.60311 ν_(d7) = 60.64 r₁₄ = −9.868 d₁₄ = 0.07r₁₅ = 25.676 d₁₅ = 0.37 n_(d8) = 1.84666 ν_(d8) = 23.78 r₁₆ = 2.938 d₁₆= (Variable) r₁₇ = 7.544 d₁₇ = 0.91 n_(d9) = 1.58913 ν_(d9) = 61.14 r₁₈= −46.010

Zooming Spaces

f  2.924  5.049  8.425 d₃ 0.36 2.53 4.14 d₉ 4.46 2.29 0.69 d₁₀ 2.85 1.700.50 d₁₆ 1.02 1.85 1.88

Aspherical Coefficients

11 th surface

K=−0.218

A ₄=−4.79076×10⁻³

A ₆=7.18792×10⁻⁴

A ₈=−2.84416×10⁻⁴

A ₁₀=4.21243×10⁻⁵

|F ₂ /F ₃|=0.837

F ₃ /F ₄=0.475

|β_(2T)|=0.501

|L ₃ /L ₂|=0.62

(F _(3.4) w)/IH=2.58

F ₁ /IH=10.99

IH=1.8

EXAMPLE 3

f=3.238˜5.605˜9.300

F _(NO)=2.79˜3.35˜4.33

f _(B)=3.05˜3.45˜4.42

r₁ = 11.229 d₁ = 0.71 n_(d1) = 1.84666 ν_(d1) = 23.78 r₂ = 8.678 d₂ =1.82 n_(d2) = 1.60311 ν_(d2) = 60.64 r₃ = −4524.933 d₃ = (Variable) r₄ =−44.964 d₄ = 0.49 n_(d3) = 1.77250 ν_(d3) = 49.60 r₅ = 2.859 d₅ = 1.07r₆ = 10.754 d₆ = 1.04 n_(d4) = 1.80518 ν_(d4) = 25.42 r₇ = ∞ (Aspheric)d₇ = (Variable) r₈ = ∞ (Stop) d₈ = (Variable) r₉ = 4.318 (Aspheric) d₉ =1.55 n_(d5) = 1.58913 ν_(d5) = 61.18 r₁₀ = −13.012 d₁₀ = 0.09 r₁₁ =4.720 d₁₁ = 1.16 n_(d6) = 1.72916 ν_(d6) = 54.68 r₁₂ = 30.878 d₁₂ = 0.09r₁₃ = 8.260 d₁₃ = 0.41 n_(d7) = 1.84666 ν_(d7) = 23.78 r₁₄ = 2.400 d₁₄ =(Variable) r₁₅ = 5.989 (Aspheric) d₁₅ = 1.03 n_(d8) = 1.58913 ν_(d8) =61.14 r₁₆ = 666.490

Zooming Spaces

f  3.238  5.605  9.300 d₃ 0.68 3.22 4.76 d₇ 4.85 2.31 0.76 d₈ 3.32 2.130.55 d₁₄ 1.22 2.01 2.63

Aspherical Coefficients

7 th surface

K=0.000

A ₄=−2.85671×10⁻³

A ₆=−5.00585×10⁻⁶

A ₈=−4.55482×10⁻⁵

A ₁₀=1.15287×10⁻⁶

9 th surface

K=−0.218

 A ₄=−2.53050×10⁻³

A ₆=−3.22409×10⁻⁵

A ₈=1.05400×10⁻⁵

A ₁₀=−1.24302×10⁻⁶

15 th surface

K=0.000

A ₄=−1.11182×10⁻³

A ₆=2.52212×10⁻⁴

A ₈=−6.19443×10⁻⁵

A ₁₀=1.11195×10⁻⁵

|F ₂ /F ₃|=0.866

|F ₃ /F ₄|=0.591

|β_(2T)|=0.575

|L ₃ /L ₂|=0.68

(F _(3.4) w)/IH=2.52

F ₁ /IH=10.06

IH=2.0

EXAMPLE 4

f=3.144˜5.518˜9.070

F _(NO)=2.78˜3.34˜4.35

f _(B)=2.85˜3.29˜4.40

r₁ = 9.466 d₁ = 2.06 n_(d1) = 1.48749 ν_(d1) = 70.23 r₂ = 325.991 d₂ =(Variable) r₃ = 19.366 d₃ = 0.48 n_(d2) = 1.84666 ν_(d2) = 23.78 r₄ =3.135 d₄ = 1.51 r₅ = −7.920 d₅ = 0.46 n_(d3) = 1.48749 ν_(d3) = 70.23 r₆= 4.420 d₆ = 1.49 n_(d4) = 1.84666 ν_(d4) = 23.78 r₇ = 241.864 d₇ =(Variable) r₈ = ∞ (Stop) d₈ = (Variable) r₉ = 4.925 (Aspheric) d₉ = 1.91n_(d5) = 1.56384 ν_(d5) = 60.67 r₁₀ = −9.657 d₁₀ = 0.07 r₁₁ = 4.433 d₁ =1.64 n_(d6) = 1.77250 ν_(d6) = 49.60 r₁₂ = 147.741 d₁₂ = 0.40 n_(d7) =1.84666 ν_(d7) = 23.78 r₁₃ = 2.588 d₁₃ = (Variable) r₁₄ = 5.552(Aspheric) d₁₄ = 1.40 n_(d8) = 1.56384 ν_(d8) = 60.67 r₁₅ = −26.965

Zooming Spaces

f  3.144  5.518  9.070 d₂ 0.56 3.27 4.59 d₇ 4.78 2.27 0.74 d₈ 3.73 2.400.53 d₁₃ 1.29 2.16 2.95

Aspherical Coefficients

9 th surface

K=−0.218

A ₄=−1.70776×10⁻³

A ₆=3.80242×10⁻⁶

A ₈=6.65158×10⁻⁷

A ₁₀=−2.95559×10⁻⁸

14 th surface

K=0.000

A ₄=−5.91729×10⁻⁴

A ₆=−4.46239×10⁻⁵

A ₈=1.89881×10⁻⁵

A ₁₀=0

|F ₂ /F ₃|=0.779

F ₃ /F ₄=0.794

|β_(2T)|=0.586

|L ₃ /L ₂|0.792

(F _(3.4) w)/IH=2.71

F ₁ /IH9.98

IH=2.0

EXAMPLE 5

f=3.538˜6.063˜10.193

F _(NO)=1.99˜2.27˜2.71

f _(B)=3.52˜4.13˜5.01

r₁ = 11.700 d₁ = 0.75 n_(d1) = 1.80518 ν_(d1) = 25.42 r₂ = 8.376 d₂ =0.22 r₃ = 8.983 d₃ = 3.12 n_(d2) = 1.69680 ν_(d2) = 55.53 r₄ = 1994.627d₄ = (Variable) r₅ = 272.962 d₅ = 0.51 n_(d3) = 1.77250 ν_(d3) = 49.60r₆ = 3.607 d₆ = 1.90 r₇ = −67.501 d₇ = 0.51 n_(d4) = 1.48749 ν_(d4) =70.23 r₈ = 6.854 d₈ = 1.49 n_(d5) = 1.72250 ν_(d5) = 29.20 r₉ = 47.648(Aspheric) d₉ = (Variable) r₁₀ = ∞ (Stop) d₁₀ = (Variable) r₁₁ = 5.926(Aspheric) d₁₁ = 1.93 n_(d6) = 1.66910 ν_(d6) = 55.40 r₁₂ = −19.572 d₁₂= 0.09 r₁₃ = 4.844 d₁₃ = 1.64 n_(d7) = 1.67790 ν_(d7) = 55.34 r₁₄ =51.623 d₁₄ = 0.45 n_(d8) = 1.84666 ν_(d8) = 23.78 r₁₅ = 3.195 d₁₅ =(Variable) r₁₆ = 6.105 (Aspheric) d₁₆ = 1.82 n_(d9) = 1.66910 ν_(d9) =55.40 r₁₇ = −24.730

Zooming Spaces

f  3.538  6.063 10.193 d₄ 0.49 3.25 5.27 d₉ 5.60 2.83 0.84 d₁₀ 3.20 2.060.60 d₁₅ 1.45 1.97 2.55

Aspherical Coefficients

9 th surface

K=0.000

A ₄=−9.99655×10⁻⁴

A ₆=3.86110×10⁻⁵

A ₈=−1.20035×10⁻⁵

A ₁₀=6.80269×10⁻⁷

11 th surface

K=−0.218

 A ₄=−6.82101×10⁻⁴

A ₆=−1.21088×10⁻⁵

A ₈=3.20658×10⁻⁶

A ₁₀=−2.47777×10⁻⁷

16 th surface

K=0.000

A ₄=−9.45299×10⁻⁴

A ₆=2.83288×10⁻⁵

A ₈=−2.50040×10⁻⁷

A ₁₀=0

|F ₂ /F ₃|0.628

F ₃ /F ₄=1.088

|β_(2T)|=0.760

|L ₃ /L ₂|=0.54

(F _(3.4) w)/IH=2.67

F ₁ /IH=8.73

IH=2.25

EXAMPLE 6

f=2.478˜4.226˜7.162

F _(NO)=2.03˜2.36˜2.91

f _(B)=2.83˜3.44˜4.66

r₁ = 13.758 d₁ = 1.55 n_(d1) = 1.48749 ν_(d1) = 70.23 r₂ = ∞ d₂ =(Variable) r₃ = 8.156 d₃ = 0.47 n_(d2) = 1.84666 ν_(d2) = 23.78 r₄ =3.020 d₄ = 2.04 r₅ = −10.317 d₅ = 0.38 n_(d3) = 1.48749 ν_(d3) = 70.23r₆ = 3.905 d₆ = 1.69 n_(d4) = 1.84666 ν_(d4) = 23.78 r₇ = 15.206 d₇ =(Variable) r₈ = ∞ (Stop) d₈ = (Variable) r₉ = 6.594 (Aspheric) d₈ = 1.28n_(d5) = 1.58913 ν_(d5) = 61.30 r₁₀ = −13.376 d₁₀ = 0.08 r₁₁ = 3.521 d₁₁= 1.63 n_(d6) = 1.77250 ν_(d6) = 49.60 r₁₂ = 32.979 d₁₂ = 0.34 n_(d7) =1.84666 ν_(d7) = 23.78 r₁₃ = 2.478 d₁₃ = (Variable) r₁₄ = 5.082(Aspheric) d₁₄ = 1.23 n_(d8) = 1.58913 ν_(d8) = 61.30 r₁₅ = −11.553

Zooming Spaces

f  2.478  4.226  7.162 d₂ 0.38 3.62 5.92 d₇ 6.07 2.83 0.56 d₈ 3.25 2.050.56 d₁₃ 1.30 1.88 2.14

Aspherical Coefficients

9 th surface

K=0.000

A ₄=−8.83776×10⁻⁴

A ₆=−1.79814×10⁻⁴

A ₈=6.59986×10⁻⁵

A ₁₀=−8.05802×10⁻⁶

 A ₁₂=5.90942×10⁻⁸

14 th surface

K=0.000

A ₄=−1.88373×10⁻³

A ₆=−1.31653×10⁻⁴

A ₈=3.07847×10⁻⁴

A ₁₀=−33087×10⁻⁴

A ₁₂=1.81422×10⁻⁵

|F ₂ /F ₃|=0.77

F ₃ /F₄=1.12

|β_(2T)|=0.35

|L ₃ /L ₂|=0.48

(F _(3.4) w)/IH=3.06

F ₁ /IH=17.10

IH=1.5

EXAMPLE 7

f=2.976˜5.065˜8.549

F _(NO)=2.64˜3.01˜3.85

f _(B)=2.91˜3.47˜4.54

r₁ = 12.405 d₁ = 1.98 n_(d1) = 1.48749 ν_(d1) = 70.23 r₂ = ∞ d₂ =(Variable) r₃ = 15.574 d₃ = 0.45 n_(d2) = 1.84666 ν_(d2) = 23.78 r₄ =3.425 d₄ = 1.88 r₅ = −11.707 d₅ = 0.43 n_(d3) = 1.48749 ν_(d3) = 70.23r₆ = 4.402 d₆ = 1.51 n_(d4) = 1.84666 ν_(d4) = 23.78 r₇ = 34.871 d₇ =(Variable) r₈ = ∞ (Stop) d₈ = (Variable) r₉ = 4.077 (Aspheric) d₉ = 1.55n_(d5) = 1.58913 ν_(d5) = 61.28 r₁₀ = −12.990 d₁₀ = 0.09 r₁₁ = 6.194 d₁₁= 1.40 n_(d6) = 1.77250 ν_(d6) = 49.60 r₁₂ = 36.559 d₁₂ = 0.41 n_(d7) =1.84666 ν_(d7) = 23.78 r₁₃ = 2.869 d₁₃ = (Variable) r₁₄ = 7.598 d₁₄ =1.14 n_(d8) = 1.80400 ν_(d8) = 46.57 r₁₅ = −10.188 d₁₅ = 0.41 r₁₆ =−6.224 d₁₆ = 0.45 n_(d9) = 1.84666 ν_(d9) = 23.78 r₁₇ = −9.384

Zooming Spaces

f  2.976  5.065  8.549 d₂ 0.45 3.82 5.95 d₇ 6.18 2.81 0.68 d₈ 1.61 2.460.59 d₁₃ 1.07 1.67 2.49

Aspherical Coefficients

9 th surface

K=0.000

A ₄=−2.68388×10⁻³

A ₆=8.86517×10⁻⁵

A ₈=−6.80012×10⁻⁵

A ₁₀=1.65400×10⁻⁵

 A ₁₂=−1.50666×10⁻⁶

F ₂ /F ₃=0.76

F ₃ /F ₄=1.09

|β_(2T)|=0.50

|L ₃ /L ₂|=0.55

(F _(3.4) w)/IH=2.79

F ₁ /IH=12.85

IH=1.8

EXAMPLE 8

f=4.093˜7.041˜11.875

F _(NO)=2.02˜2.33˜2.80

f _(B)=4.53˜5.42˜6.90

r₁ = 18.108 d₁ = 0.94 n_(d1) = 1.84666 ν_(d1) = 23.78 r₂ = 12.307 d₂ =0.14 r₃ = 12.753 d₃ = 3.10 n_(d2) = 1.77250 ν_(d2) = 49.60 r₄ = 122.843d₄ = (Variable) r₅ = 26.311 d₅ = 0.63 n_(d3) = 1.77250 ν_(d3) = 49.60 r₆= 4.431 d₆ = 2.94 r₇ = −26.320 d₇ = 0.59 n_(d4) = 1.57250 ν_(d4) = 57.74r₈ = 4.874 d₈ = 2.27 n_(d5) = 1.80100 ν_(d5) = 34.97 r₉ = 32.145 d₉ =(Variable) r₁₀ = ∞ (Stop) d₁₀ = (Variable) r₁₁ = 8.399 (Aspheric) d₁₁ =1.78 n_(d6) = 1.58913 ν_(d6) = 61.30 r₁₂ = −20.918 d₁₂ = 0.13 r₁₃ =10.353 d₁₃ = 3.13 n_(d7) = 1.77250 ν_(d7) = 49.60 r₁₄ = −5.691 d₁₄ =0.56 n_(d8) = 1.68893 ν_(d8) = 31.07 r₁₅ = 4.778 d₁₅ = (Variable) r₁₆ =8.696 (Aspheric) d₁₆ = 3.13 n_(d9) = 1.58913 ν_(d9) = 61.30 r₁₇ =−16.508

Zooming Spaces

f  4.093  7.041 11.875 d₄ 0.63 4.63 7.56 d₉ 7.87 3.87 0.94 d₁₀ 4.43 2.750.84 d₁₅ 1.26 2.05 2.48

Aspherical Coefficients

11 th surface

K=0.000

A ₄=−4.74324×10⁻⁴

A ₆=−2.42146×10⁻⁵

A ₈=2.49585×10⁻⁶

A ₁₀=−1.17216×10⁻⁷

16 th surface

K=0.000

A ₄=−6.18094×10⁻⁴

A ₆=−7.96643×10⁻⁵

A ₈=−1.16593×10⁻⁶

A ₁₀=−6.32501×10⁻⁷

|F ₂ /F ₃|0.64

 F ₃ /F ₄=1.07

|_(2T)|=0.56

|L ₃ /L ₂|=0.52

(F _(3.4) w)/IH=2.81

F ₁ /IH=10.96

IH=2.5

EXAMPLE 9

f=3.281˜5.633˜9.500

F _(NO)=2.03˜2.41˜2.98

f _(B)=2.98˜3.50˜4.60

r₁ = 13.782 d₁ = 0.90 n_(d1) = 1.84666 ν_(d1) = 23.78 r₂ = 11.125 d₂ =2.64 n_(d2) = 1.69680 ν_(d2) = 55.53 r₃ = 73.145 d₃ = (Variable) r₄ =16.578 d₄ = 0.60 n_(d3) = 1.84666 ν_(d3) = 23.78 r₅ = 3.821 d₅ = 2.97 r₆= −16.432 d₆ = 0.47 n_(d4) = 1.58913 ν_(d4) = 61.14 r₇ = 4.721 d₇ = 2.50n_(d5) = 1.84666 ν_(d5) = 23.78 r₈ = 36.357 d₈ = (Variable) r₉ = ∞(Stop) d₉ = (Variable) r₁₀ = 6.997 (Aspheric) d₁₀ = 2.32 n_(d6) =1.58913 ν_(d6) = 61.30 r₁₁ = −13.157 d₁₁ = 0.10 r₁₂ = 5.948 d₁₂ = 2.50n_(d7) = 1.77250 ν_(d7) = 49.60 r₁₃ = −9.882 d₁₃ = 0.45 n_(d8) = 1.80518ν_(d8) = 25.42 r₁₄ = 3.525 d₁₄ = (Variable) r₁₅ = 6.328 (Aspheric) d₁₅ =2.50 n_(d9) = 1.58913 ν_(d9) = 61.30 r₁₆ = −18.262

Zooming Spaces

f  3.281  5.633  9.500 d₃ 0.50 3.55 5.78 d₈ 6.03 2.99 0.75 d₉ 3.91 2.440.68 d₁₄ 0.64 1.59 2.27

Aspherical Coefficients

10 th surface

K=0.000

A ₄=−6.74025×10⁻⁴

A ₆=−3.39527×10⁻⁵

A ₈=6.17490×10⁻⁶

A ₁₀=−3.69154×10⁻⁷

15 th surface

K=0.000

A ₄=−1.22978×10⁻³

A ₆=2.57259×10⁻⁴

A ₈=−5.94053×10⁻⁵

A ₁₀=5.10256×10⁻⁵

|F ₂ /F ₃|=0.72

F ₃ /F ₄0.96

|β_(2T)|=0.55

|L ₃ /L ₂|=0.61

 (F _(3.4) w)/IH=2.73

F ₁ /IH=11.41

IH=2.0

EXAMPLE 10

f=3.634˜6.338˜10.687

F _(NO)=2.03˜2.36˜2.86

f _(B)=4.06˜5.03˜6.69

r₁ = 25.537 d₁ = 0.84 n_(d1) = 1.84666 ν_(d1) = 23.78 r₂ = 17.128 d₂ =1.92 n_(d1) = 1.77250 ν_(d2) = 49.60 r₃ = 41.101 d₃ = 0.11 r₄ = 17.177d4 = 2.25 n_(d1) = 1.60311 ν_(d3) = 60.64 r₅ = 64.686 d₅ = (Variable) r₆= 21.366 d₆ = 0.56 n_(d1) = 1.80610 ν_(d4) = 40.92 r₇ = 4.013 d₇ = 2.78r₈ = −19.517 d₈ = 0.53 n_(d1) = 1.59551 ν_(d5) = 39.24 r₉ = 4.450 d₉ =2.10 n_(d1) = 1.80518 ν_(d6) = 25.42 r₁₀ = 34.830 d₁₀ = (Variable) r₁₁ =∞ (Stop) d₁₁ = (Variable) r₁₂ = 11.333 (Aspheric) d₁₂ = 2.15 n_(d1) =1.58913 ν_(d7) = 61.30 r₁₃ = −15.421 d₁₃ = 0.11 r₁₄ = 6.624 d₁₄ = 2.81n_(d1) = 1.77250 ν_(d8) = 49.60 r₁₅ = −9.336 d₁₅ = 0.51 n_(d1) = 1.74077ν_(d9) = 27.79 r₁₆ = 4.319 d₁₆ = (Variable) r₁₇ = 8.127 (Aspheric) d₁₇ =2.81 n_(d1) = 1.58913 ν_(d10) = 61.30 r₁₈ = −13.550

Zooming Spaces

f  3.634  6.338 10.687 d₅ 0.56 4.10 6.61 d₁₀ 6.89 3.35 0.84 d₁₁ 4.432.65 0.76 d₁₆ 1.66 2.46 2.70

Aspherical Coefficients

12 th surface

K=0.000

A ₄=−2.72290×10⁻⁴

A ₆=−2.67214×10⁻⁵

A ₈=3.52082×10⁻⁶

A ₁₀=−1.72643×10⁻⁷

17 th surface

K=0.000

A ₄=−6.98015×10⁻⁴

A ₆=8.08033×10⁻⁵

A ₈=−1.17442×10⁻⁵

A ₁₀=6.68163×10⁻⁷

|F ₂ /F ₃|=0.59

F ₃/ F₄=1.08

|β_(2T)|=0.55

|L ₃ /L ₂|=0.61

(F _(3.4) w)/IH=2.96

 F ₁ /IH=11.19

IH=2.25

FIGS. 12 and 13 are aberration diagrams for Example 1 of the presentzoom lens system at the wide-angle and telephoto ends, respectively,upon focused on an object point at infinity. In these drawings, (a),(b), (c), (d) and (e) represent spherical aberrations, astigmatism,distortion, chromatic aberration of magnification and coma,respectively. It is noted that ω stands for a half field angle.

The zoom lens system according to the present invention may be used onvarious image pickup systems using electronic image pickup devices suchas CCD or CMOS sensors, as embodied below.

An electronic cameral wherein the zoom lens system of the presentinvention is incorporated in the form of an objective optical system isshown in FIGS. 14 to 16. FIG. 14 is a front perspective viewillustrative of the appearance of an electronic camera 200, and FIG. 15is a rear perspective view illustrative of the electronic camera 200.FIG. 16 is a sectional view illustrative of the construction of theelectronic camera 200. As shown in FIGS. 14 to 16, the electronic camera200 comprises a phototaking optical system 202 including a phototakingoptical path 201, a finder optical system 204 including a finder opticalpath 203, a shutter 205, a flash 206 and a liquid crystal displaymonitor 207. Upon pressing down the shutter 205 located on the upperportion of the camera 200, phototaking occurs through an objective lenssystem 12 comprising the instant zoom lens system (roughly shown)located as a phototaking objective optical system. An object imageformed through the phototaking optical system is then formed on theimage pickup plane of an image pickup device chip 62 such as a CCD viaan IR (infrared rays) cut filter 80.

The object image sensed by image pickup device chip 62 is displayed asan electronic image on the liquid crystal display monitor 207 located onthe back side of the camera via processing means 208 electricallyconnected to a terminal 66. This processing means 208 may also controlrecording means 209 for recording the object image phototaken throughthe image pickup device chip 62 in the form of electronic information.It is here noted that the recording means 209 may be provided as amemory mounted on the processing means 208 or in the form of a deviceelectrically connected to the processing means 208 to electronicallywrite the information into a magnetic recording medium such as a floppydisk or smart media.

Further, the finder optical system 204 having a finder optical path 203comprises a finder objective optical system 210, a Porro prism 211 forerecting the object image formed through the finder objective opticalsystem 210 and an eyepiece 212 for guiding the object image to theeyeball E of an observer. The Porro prism 211 is divided into a frontand a rear block with an object image-forming surface located betweenthem. The Porro prism 211 comprises four reflecting surfaces to erectthe object image formed through the finder objective optical system 204.

To reduce the number of parts and achieve compactness and costreductions, the finder optical system 204 may be removed from the camera200. In this case, the observer carries out phototaking while looking atthe liquid crystal monitor 207.

Shown in FIGS. 17 to 19 is a personal computer that is one example ofthe information processor in which the zoom lens system of the inventionis incorporated in the form of an objective optical system. FIG. 17 is afront perspective views of an uncovered personal computer 300, FIG. 18is a sectional view of a phototaking optical system 303 mounted on thepersonal computer 300, and FIG. 19 is a side view of FIG. 17. Asdepicted in FIGS. 17 to 19, the personal computer 300 comprises a keyboard 301 for allowing an operator to enter information therein fromoutside, information processing and recording means (not shown), amonitor 302 for displaying the information to the operator and aphototaking optical system 303 for phototaking an image of the operatorper se and images of operator's surroundings. The monitor 302 usedherein may be a transmission type liquid crystal display device designedto be illuminated by a backlight (not shown) from the back side, areflection type liquid crystal display device designed to display imagesby reflecting light from the front side, a CRT display or the like. Asshown, the phototaking optical system 303 is built in a right upperportion of monitor 302. However, it is to be understood that thephototaking optical system 303 may be positioned somewhere on theperiphery of monitor 302 or keyboard 301.

The phototaking optical system 303 includes on a phototaking opticalpath 304 an objective lens system 12 comprising the zoom lens system ofthe invention (roughly shown) and an image pickup device chip 62 forreceiving an image. These are built in the personal computer 300.

An object image sensed by the image pickup device chip 62 is enteredfrom a terminal 66 in the processing means in the personal computer 300,and displayed as an electronic image on the monitor 302. Shown in FIG.17 as an example is a phototaken image 305 of the operator. It ispossible to display the image 305, etc. on a personal computer at theother end on a remote place via an internet or telephone line.

Illustrated in FIG. 20 is a telephone handset that is one example of theinformation processor in which the zoom lens system of the invention isbuilt in the form of a phototaking optical system, especially aconvenient-to-carry portable telephone handset. FIG. 20(a) is a frontview of a portable telephone handset 400, FIG. 20(b) is a side view ofhandset 400 and FIG. 20(c) is a sectional view of a phototaking opticalsystem 405. As depicted in FIGS. 20(a) to 20(c), the telephone handset400 comprises a microphone portion 401 for entering an operator's voicetherein as information, a speaker portion 402 for producing a voice of aperson on the other end, an input dial 403 allowing the operator toenter information therein, a monitor 404 for displaying phototakenimages of the operator and the person on the other end and informationsuch as telephone numbers, a phototaking optical system 405, an antenna406 for transmitting and receiving communication waves and a processingmeans (not shown) for processing image information, communicationinformation, input signals, etc. The monitor 404 used herein is a liquidcrystal display device. The arrangement of these parts is notnecessarily limited to that illustrated. The phototaking optical system405 includes on a phototaking optical path 407 an objective lens system12 comprising the zoom lens system (roughly illustrated) of theinvention and an image pickup device chip 62 for receiving an objectimage. These are built in the telephone handset 400.

The object image sensed by the image pickup device chip 62 is enteredfrom a terminal 66 in a processing means (not shown), and displayed asan electronic image on the monitor 404 and/or a monitor on the otherend. To transmit an image to a person on the other end, the processingmeans includes a signal processing function of converting informationabout the object image received at the image pickup element chip 62 totransmittable signals.

According to the present invention as explained above, it is thuspossible to achieve a compact yet low-cost zoom lens system, andespecially a zoom lens system suitable for use on portable informationterminals of small size.

I claim:
 1. An image pickup system including a finder optical system, adisplay monitor, and an objective optical system comprising a zoom lenssystem and an electronic image pickup device located on an image side ofsaid zoom lens system, an object image sensed by said pickup device isdisplayed as an electronic image on said display monitor, wherein saidzoom lens system comprises, in order from the object side of said zoomlens, a first lens group having positive refracting power, a second lensgroup having negative refracting power and designed to move from theobject side to an image plane side of the zoom lens system for zoomingfrom a wide-angle end to a telephoto end of said zoom lens system, athird lens group having positive refracting power and designed to movefrom the image plane side to the object side for zooming from the wideangle end to the telephoto end, and fourth lens group having positiverefracting power and designed to be movable for zooming, wherein saidfirst lens group consists of a positive lens component, wherein saidsecond lens group consists of, in order from the object side, a negativelens element convex toward the object side, a bi-concave negative lenselement, and a positive lens element convex toward the object side,wherein said third lens group consists of, in order from the objectside, a positive single lens component convex to the object side, and acemented lens component including a bi-convex lens element and abi-concave lens element, and wherein said fourth lens group consists ofa positive single lens component convex to the object side.
 2. An imagepickup system including an objective optical system comprising a zoomlens system and an electronic image pickup device located on an imageside of said zoom lens system, wherein said zoom lens system comprising,in order from an object side of said zoom lens system, a first lensgroup having positive refracting power and designed to be fixed duringzooming, a second lens group having negative refracting power anddesigned to move from the object side to an image plane side of saidzoom lens system for zooming from a wide-angle end to a telephoto end ofsaid zoom lens system, a third lens group having positive refractingpower and designed to move from the image plane side to the object sidefor zooming from the wide-angle end to the telephoto end, and a fourthlens group having positive refracting power and designed to be movablefor zooming wherein the following conditions are satisfied: 0.49<|L 3 /L2|<1  (2) 2.5 mm<fB(min)<4.8 mm  (10) where Li is an amount of movementof an i-th lens group from the wide-angle end to the telephoto end andfB(min) is a length, as calculated on an air basis, of a final surfaceof a lens having power in said zoom lens system to an image plane ofsaid zoom lens system, representing a figure at which said zoom lenssystem becomes shortest in a whole zooming space.
 3. An image pickupsystem including an objective optical system comprising a zoom lenssystem and an electronic image pickup device located on an image side ofsaid zoom lens system, wherein said zoom lens system comprising, inorder from an object side of said zoom lens system, a first lens grouphaving positive refracting power and designed to be fixed duringzooming, a second lens group having negative refracting power anddesigned to move from the object side to an image plane side of the zoomlens system for zooming from a wide-angle end to a telephoto end of saidzoom lens system, a third lens group having positive refracting powerand designed to move from the object side to the image plane side forzooming from the wide-angle end to the telephoto end, and a fourth lensgroup having positive refracting power and designed to be movable forzooming wherein the following conditions are satisfied: 2<(F 3.4W)/IH<3.3  (3) 2.5 mm<fB(min)<4.8 mm  (10) where (F3.4W) is a compositefocal length of the third and fourth lens groups at the wide angle end,IH is a radius of an image circle, and fB(min) is a length, ascalculated on an air basis, of a final surface of a lens having power insaid zoom lens system to an image plane of said zoom lens system,representing a figure at which said zoom lens system becomes shortest ina whole zooming space.
 4. An image pickup system including an objectiveoptical system comprising a zoom lens system and an electronic imagepickup device located on an image side of said zoom lens system, whereinsaid zoom lens system comprising, in order from an object side of saidzoom lens system, a first lens group having positive refracting power, asecond lens group having negative refracting power and designed to movefrom the object side to an image plane side of said zoom lens system forzooming from a wide-angle end to a telephoto end of said zoom lenssystem, a third lens group having positive refracting power and a fourthlens group having positive refracting power and designed to be movablefor zooming, wherein said third lens group comprises, in order from anobject side thereof, a positive lens component convex on an object sidethereof and a cemented lens consisting of a positive lens element convexon an object side thereof and a negative lens element concave on animage plane side thereof, and both the object-side positive lenscomponent and the cemented lens in said third lens group are held in alens barrel while the object-side convex surfaces thereof abutperipherally or at peripheral several spots against said lens barrel,and the following condition is satisfied: 2.5 mm<fB(min)<4.8 mm  (10)where fB(min) is a length, as calculated on an air basis, of a finalsurface of a lens having power in said zoom lens system to an imageplane of said zoom lens system, representing a figure at which said zoomlens system becomes shortest in a whole zooming space.
 5. An imagepickup system including an objective optical system comprising a zoomlens system and an electronic image pickup device located on an imageside of said zoom lens system, wherein said zoom lens system comprising,in order from an object side of said zoom lens system, a first lensgroup having positive refracting power and designed to be fixed duringzooming, a second lens group having negative refracting power anddesigned to move from the object side to an image plane side of the zoomlens system for zooming from a wide-angle end to a telephoto end of saidzoom lens system, a third lens group having positive refracting powerand designed to move from the image plane side to the object side forzooming from the wide-angle end to the telephoto end, and a fourth lensgroup having positive refracting power and designed to be movable forzooming, wherein the following conditions are satisfied: 0.5<|F 2 /F3|<1.2  (1) 0.49<|L 3 /L 2|<1  (2) 2.5 mm<fB(min)<4.8 mm  (10) where Fiis a focal length of an i-th lens group, Li is an amount of an i-th lensgroup from the wide-angle end to the telephoto end, and fB(min) is alength, as calculated on an air basis, of a final surface of a lenshaving power in said zoom lens system to an image plane of said zoomlens system, representing a figure at which said zoom lens systembecomes shortest in a whole zooming space.
 6. An image pickup systemincluding an objective optical system comprising a zoom lens system andan electronic image pickup device located on an image side of said zoomlens system, wherein said zoom lens system comprising, in order from anobject side of said zoom lens system, a first lens group having positiverefracting power and designed to be fixed during zooming, a second lensgroup having negative refracting power and designed to move from theobject side to an image plane side of the zoom lens system for zoomingfrom a wide-angle end to a telephoto end of said zoom lens system, athird lens group having positive refracting power and designed to movefrom the image plane side to the object side for zooming from thewide-angle end to the telephoto end, and a fourth lens group havingpositive refracting power and designed to be movable for zooming,wherein the following conditions are satisfied: 0.5<|F 2 /F 3|<1.2  (1)2<(F 3.4 W)/IH<3.3  (3) 2.5 mm<fB(min)<4.8 mm  (10) where Fi is a focallength of an i-th lens group, (F3.4W) is a composite focal length of thethird and fourth lens groups at the wide-angle end, IH is a radius of animage circle, and fb(min) is a length, as calculated on an air basis, ofa final surface of a lens having power in said zoom lens system to animage plane of said zoom lens system, representing a figure at whichsaid zoom lens system becomes shortest in a whole zooming space.
 7. Animage pickup system including an objective optical system comprising azoom lens system and an electronic image pickup device located on animage side of said zoom lens system, wherein said zoom lens systemcomprising, in order from an object side of said zoom lens system, afirst lens group having positive refracting power and designed to befixed during zooming, a second lens group having negative refractingpower and designed to move from the object side to an image plane sideof the zoom lens system for zooming from a wide-angle end to a telephotoend of said zoom lens system, a third lens group having positiverefracting power and designed to move from the image plane side to theobject side for zooming from the wide-angle end to the telephoto end,and a fourth lens group having positive refracting power and designed tobe movable for zooming wherein the following conditions are satisfied:0.49<|L 3 /L 2|<1  (2) 2<(F 3.4 W)/IH<3.3  (3) 2.5 mm<fB(min)<4.8mm  (10) where Li is an amount of movement of an i-th lens group,(F3.4w) is a composite focal length of the third and fourth lens groupsat the wide-angle end, IH is a radius of an image circle, and fB(min) isa length, as calculated on an air basis, of a final surface of a lenshaving power in said zoom lens system to an image plane of said zoomlens system, representing a figure at which said zoom lens systembecomes shortest in a whole zooming space.
 8. An image pickup systemincluding an objective optical system comprising a zoom lens system andan electronic image pickup device located on an image side of said zoomlens system, wherein said zoom lens system comprising, in order from anobject side of said zoom lens system, a first lens group having positiverefracting power and designed to be fixed during zooming, a second lensgroup having negative refracting power and designed to move from theobject side to an image plane side of the zoom lens system for zoomingfrom a wide-angle end to a telephoto end of said zoom lens system, athird lens group having positive refracting power and designed to movefrom the image plane side to the object side for zooming from thewide-angle end to the telephoto end, and a fourth lens group havingpositive refracting power and designed to be movable for zooming,wherein the following conditions are satisfied: 0.5<|F 2 /F 3|<1.2  (1)0.49<|L 3 /L 2|<1  (2) 2<(F 3.4 W)/IH<3.3  (3) 2.5 mm<fB(min)<4.8mm  (10) where Fi is a focal length of an i-th lens group, Li is anamount of movement of an i-th lens group, (F3.4W) is a composite focallength of the third and fourth lens groups at the wide-angle end, IH isa radius of an image circle, and fB(min) is a length, as calculated onan air basis, of a final surface of a lens having power in said zoomlens system to an image plane of said zoom lens system, representing afigure at which said zoom lens system becomes shortest in a wholezooming space.
 9. The image pickup system according to any one of claims1, 2, 3 and 5 to 8, wherein said zoom lens system satisfies thefollowing condition: 0.6<|F 2 /F 3|<1  (4) where Fi is the focal lengthof an i-th lens group.
 10. The image pickup system according to any oneof claims 1, 2, 3, and 5 to 8, wherein said fourth lens group is movedin an optical axis direction for focusing.
 11. The image pickup systemaccording to any one of claims 1, 2, 3, and 5 to 8, wherein said zoomlens system satisfies the following condition: 0.3<|F 3 /F 4|<0.8  (5)where Fi is the focal length of an i-th lens group.
 12. The image pickupsystem according to any one of claims 1, 2, 3, and 5 to 8, wherein saidzoom lens system satisfies the following condition: 0.4<|β2T|<1  (6)where β2T is a transverse magnification of the second lens group. 13.The image pickup system according to any one of claims 1, 2, 3, and 5 to8, wherein said fourth lens group consists of one positive lens element.14. The image pickup system according to any one of claims 1, 2, 3, and5 to 8, wherein said third lens group consists of three lenses elementsor a positive lens element, a positive lens element and a negative lenselement in order from an object side thereof.
 15. The image pickupsystem according to any one of claims 1, 2, 3, and 5 to 8, wherein atleast one surface in said third lens group is defined by an asphericalsurface.
 16. The image pickup system according to any one of claims 1,2, 3, and 5 to 8, wherein at least one surface in said fourth lens groupis defined by an aspherical surface.
 17. The image pickup systemaccording to any one of claims 1, 2, 3, and 5 to 8, wherein at least onesurface in said second lens group is defined by an aspherical surface.18. An image pickup system including an objective optical systemcomprising a zoom lens system and an electronic image pickup devicelocated on an image side of said zoom lens system, wherein said zoomlens system comprising, in order from an object side of said zoom lenssystem, a first lens group having positive refracting power and designedto be fixed during zooming, a second lens group having negativerefracting power and designed to move from the object side to an imageplane side of the zoom lens system for zooming from a wide-angle end toa telephoto end of said zoom lens system, a third lens group havingpositive refracting power and designed to move from the image plane sideto the object side for zooming from the wide-angle end to the telephotoend, and a fourth lens group having positive refracting power anddesigned to be movable for zooming, wherein said first lens groupconsists of one positive lens element, a lens element located nearest tothe object side in said second lens group is defined by a negative lenselement, and the following conditions are satisfied: ν21<40  (7) 2.5mm<fB(min)<4.8 mm  (10) where ν21 is an Abbe's number of said negativelens element located nearest to the object side in said second lensgroup, and fB(min) is a length, as calculated on an air basis, of afinal surface of a lens having power in said zoom lens system to animage plane of said zoom lens system, representing a figure at whichsaid zoom lens system becomes shortest in a whole zooming space.
 19. Theimage pickup system according to claim 18, which satisfies the followingcondition: ν21<35  (8)
 20. The image pickup system according to any oneof claims 1, 2, 3, and 5 to 8, wherein a lens element located nearest tothe object side in said second lens group is defined by a negative lenselement, and the following condition is satisfied: ν21<40  (7) where ν₂₁is an Abbe's number of said negative lens element located nearest to theobject side in said lens group.
 21. The image pickup system according toclaim 20, which satisfies the following condition: ν21<35  (8) where ν21is an Abbe's number of said negative lens element located nearest to theobject side in said second lens group.
 22. The image pickup systemaccording to any one of claims 1, 2, 5 to 8, 18 and 19, wherein saidthird lens group comprises, in order from an object side thereof, apositive lens component convex on an object side thereof and a cementedlens consisting of a positive lens element convex on an object sidethereof and a negative lens element concave on an image side thereof,and said cemented lens and said positive lens on the object side areheld in a lens barrel while the peripheral edges of the convex surfacesthereof abut peripherally or at a peripheral several spots against thelens barrel.
 23. An image pickup system including an objective opticalsystem comprising a zoom lens system and an electronic image pickupdevice located on an image side of said zoom lens system, wherein saidzoom lens system comprising, in order from an object side of said zoomlens system, a first lens group having positive refracting power anddesigned to be fixed during zooming, a second lens group having negativerefracting power and designed to move from the object side to an imageplane side of the zoom lens system for zooming from a wide-angle end toa telephoto end of said zoom lens system, a third lens group havingpositive refracting power and designed to move constantly from the imageplane side to the object side for zooming from the wide-angle end to thetelephoto end, and a fourth lens group having positive refracting powerand designed to be movable during zooming, wherein said third lens groupcomprises a cemented lens consisting of a positive lens element and anegative lens element, said fourth lens group consists of one positivelens element, and the following conditions are satisfied: 2.5mm<fB(min)<4.8 mm  (10) where fB(min) is a length, as calculated on anair basis, of a final surface of a lens having power in said zoom lenssystem to an image plane of said zoom lens system, representing a figureat which said zoom lens system becomes shortest in a whole zoomingspace.
 24. The image pickup system according to claim 23, wherein atleast one surface of said positive lens in said fourth lens group isdefined by an aspherical surface.
 25. An image pickup system includingan objective optical system comprising a zoom lens system and anelectronic image pickup device located on an image side of said zoomlens system, wherein said zoom lens system comprising, in order from anobject side of said zoom lens system, a first lens group having positiverefracting power and designed to be fixed during zooming, a second lensgroup having negative refracting power and designed to move from theobject side to an image plane side of the zoom lens system for zoomingfrom a wide-angle end to a telephoto end of said zoom lens system, athird lens group having positive refracting power and designed to moveconstantly from the image plane side to the object side for zooming fromthe wide-angle end to the telephoto end, and a fourth lens group havingpositive refracting power and designed to be movable during zooming,wherein said second lens group, and said third lens group comprises acemented lens consisting of a positive lens element and a negative lenselement, and the following condition (10) is satisfied: 2.5mm<fB(min)<4.8 mm  (10) where fB(min) is a length, as calculated on anair basis, of a final surface of a lens having power in said zoom lenssystem to an image plane of said zoom lens system, representing a figureat which said zoom lens system becomes shortest in a whole zoomingspace.
 26. An image pickup system including an objective optical systemcomprising a zoom lens system and an electronic image pickup devicelocated on an image side of said zoom lens system, wherein said zoomlens system comprising, in order from an object side of said zoom lenssystem, a first lens group having positive refracting power and designedto be fixed during zooming, a second lens group having negativerefracting power and designed to move from the object side to an imageplane side of the zoom lens system for zooming from a wide-angle end toa telephoto end of said zoom lens system, a third lens group havingpositive refracting power and designed to move constantly from the imageplane side to the object side for zooming from the wide-angle end to thetelephoto end, and a fourth lens group having positive refracting powerand designed to be movable during zooming, wherein said third lens groupcomprises, in order from an object side thereof, a positive lenscomponent and a cemented lens consisting of a positive lens element anda negative lens element, and the following condition (10) is satisfied:2.5 mm<fB(min)<4.8 mm  (10) where fB(min) is a length, as calculated onan air basis, of a final surface of a lens having power in said zoomlens system to an image plane of said zoom lens system, representing afigure at which said zoom lens system becomes shortest in a wholezooming space.
 27. An image pickup system including an objective opticalsystem comprising a zoom lens system and an electronic image pickupdevice located on an image side of said zoom lens system, wherein saidzoom lens system comprising, in order from an object side of said zoomlens system, a first lens group having positive refracting power, asecond lens group having negative refracting power, a third lens grouphaving positive refracting power, and a fourth lens group havingpositive refracting power, wherein a spacing between said first lensgroup and said second lens group, a spacing between said second lensgroup and said third lens group, and a spacing between said third lensgroup and said fourth lens group varies upon zooming, said third lensgroup comprises, in order from an object side thereof, a double-convexpositive lens component and a cemented lens consisting of a positivemeniscus lens element convex on an object side thereof and a negativemeniscus lens element, said fourth lens group comprises a double-convexlens element in which an object-side surface thereof has a largercurvature, and the following condition (10) is satisfied: 2.5mm<fB(min)<4.8 mm  (10) where fB(min) is a length, as calculated on anair basis, of a final surface of a lens having power in said zoom lenssystem to an image plane of said zoom lens system, representing a figureat which said zoom lens system becomes shortest in a whole zoomingspace.
 28. An image pickup system including an objective optical systemcomprising a zoom lens system and an electronic image pickup devicelocated on an image side of said zoom lens system, wherein said zoomlens system comprising, in order from an object side of said zoom lenssystem, a first lens group having positive refracting power, a secondlens group having negative refracting power, a third lens group havingpositive refracting power, and a fourth lens group having positiverefracting power, wherein a spacing between said first lens group andsaid second lens group, a spacing between said second lens group andsaid third lens group, and a spacing between said third lens group andsaid fourth lens group varies upon zooming, said first lens groupconsists of one positive lens component, said second lens groupcomprises three lens elements or one single lens element and a cementedlens consisting of a negative lens element and a positive lens elementin order from an object side thereof, said third lens group comprisesthree lens elements or a single lens element and a cemented lensconsisting of a positive lens element and a negative lens element inorder from an object side thereof, said fourth lens group consists ofone positive lens element, and the following condition (10) issatisfied: 2.5 mm<fB(min)<4.8 mm  (10) where fB(min) is a length, ascalculated on an air basis, of a final surface of a lens having power insaid zoom lens system to an image plane of said zoom lens system,representing a figure at which said zoom lens system becomes shortest ina whole zooming space.
 29. An image pickup system including an objectiveoptical system comprising a zoom lens system and an electronic imagepickup device located on an image side of said zoom lens system, whereinsaid zoom lens system comprising, in order from an object side of saidzoom lens system, a first lens group having positive refracting power, asecond lens group having negative refracting power, a third lens grouphaving positive refracting power, and a fourth lens group havingpositive refracting power, wherein a spacing between said first lensgroup and said second lens group, a spacing between said second lensgroup and said third lens group, and a spacing between said third lensgroup and said fourth lens group varies upon zooming, said first lensgroup comprises two lens elements or a positive lens element and anegative lens element, said second or said third lens group includestherein a cemented lens component consisting of at least one set of apositive lens element and a negative lens element, and the followingcondition (10) is satisfied: 2.5 mm<fB(min)<4.8 mm  (10) where fB(min)is a length, as calculated on an air basis, of a final surface of a lenshaving power in said zoom lens system to an image plane of said zoomlens system, representing a figure at which said zoom lens systembecomes shortest in a whole zooming space.
 30. An image pickup systemincluding an objective optical system comprising a zoom lens system andan electronic image pickup device located on an image side of said zoomlens system, wherein said zoom lens system comprising, in order from anobject side of said zoom lens system, a first lens group having positiverefracting power and designed to be fixed during zooming, a second lensgroup having negative refracting power and designed to move from theobject side to an image plane side of the zoom lens system for zoomingfrom a wide-angle end to a telephoto end of said zoom lens system, athird lens group having positive refracting power and designed to moveconstantly from the image plane side to the object side for zooming fromthe wide-angle end to the telephoto end, and a fourth lens groupconsists of one lens element, having positive refracting power anddesigned to be movable during zooming, wherein said second lens group,and said third lens group comprises a cemented lens component consistingof a positive lens element and a negative lens element, and image sidesurface of said cemented lens component in said second lens group isconcave surface, and said third lens group or said fourth lens groupincludes therein at least one aspherical surface.
 31. An image pickupsystem including an objective optical system comprising a zoom lenssystem and an electronic image pickup device located on an image side ofsaid zoom lens system, wherein said zoom lens system comprising, inorder from an object side of said zoom lens system, a first lens grouphaving positive refracting power, a second lens group having negativerefracting power, a third lens group having positive refracting power,and a fourth lens group having positive refracting power, wherein aspacing between said first lens group and said second lens group, aspacing between said second lens group and said third lens group, and aspacing between said third lens group and said fourth lens group variesupon zooming, said first lens group consists of one positive lenscomponent, said second lens group comprises three lens elements or asingle lens element and a cemented lens consisting of a negative lenselement and a positive lens element in order from an object sidethereof, said third lens group comprises three lens elements or a singlelens element and a cemented lens consisting of a positive lens elementand a negative lens, and said fourth lens group consists of one positivelens element, with at least one aspherical surface introduced in saidthird lens group or said fourth lens group, and an image side surface ofsaid cemented lens in said second lens group is concave surface.
 32. Theimage pickup system according to any one of claims 1 to 8, 21, 23 and 25to 31, wherein said zoom lens system satisfies the following condition:2.5 mm<fB(max)<4.8 mm  (11) where fB(max) is a length, as calculated onan air basis, of a final surface of a lens having power in said zoomlens system to an image plane of said zoom lens system, representing afigure at which said zoom lens system becomes longest in a whole zoomingspace.
 33. An image pickup system including a finder optical system, adisplay monitor, and an objective optical system comprising a zoom lenssystem and an electronic image pickup device located on an image side ofsaid zoom lens system, and an object image sensed by said image pickupdevice is displayed as an electronic image on said display monitor,wherein said zoom lens system comprising, in order from the object sideof said zoom lens, a first lens group having positive refracting power,a second lens group having negative refracting power and designed tomove from the object side to an image plane side of the zoom lens systemfor zooming from a wide-angle end to a telephoto end of said zoom lenssystem, a third lens group having positive refracting power and designedto move from the image plane side to the object side for zooming fromthe wide-angle end to the telephoto end, and a fourth lens group havingpositive refracting power and designed to be movable for zooming,wherein said first lens group consists of a positive lens component,wherein said second lens group consists of, in order from the objectside, a negative lens element convex toward the object side, abi-concave negative lens element, and a positive lens element convextoward the object side wherein said third lens group consists of, inorder from the object side, a bi-convex single lens component, acemented lens component including a bi-convex lens element and abi-concave lens element, and wherein said fourth lens group consists ofa positive single lens component convex to the object side.
 34. Theimage pickup system according to claim 33, wherein the followingcondition is satisfied: 0.5<|F 2 /F 3|<1.2  (1).
 35. The image pickupsystem according to claim 33, wherein the following condition issatisfied: 0.49<|L 3 /L 2|<1  (2).
 36. The image pickup system accordingto claim 33, wherein the following condition is satisfied: 2<(F 3.4W)/IH<3.3 mm  (3).
 37. The image pickup system according to claim 33,wherein the following condition is satisfied: 0.6<|F 2 /F 3|<1  (4). 38.The image pickup system according to claim 33, wherein the followingcondition is satisfied: 0.3<|F 3 /F 4|<0.8  (5).
 39. The image pickupsystem according to claim 33, wherein the following condition issatisfied: 0.4<|β2T|<1  (6).
 40. The image pickup system according toclaim 33, wherein the following condition is satisfied: ν21<40  (7). 41.The image pickup system according to claim 33, wherein the followingcondition is satisfied: ν21<35  (8).